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diff --git a/15283.txt b/15283.txt new file mode 100644 index 0000000..b785543 --- /dev/null +++ b/15283.txt @@ -0,0 +1,6148 @@ +The Project Gutenberg eBook, Disease and Its Causes, by William Thomas +Councilman + + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + + + + +Title: Disease and Its Causes + +Author: William Thomas Councilman + +Release Date: March 8, 2005 [eBook #15283] + +Language: English + +Character set encoding: ISO-646-US (US-ASCII) + + +***START OF THE PROJECT GUTENBERG EBOOK DISEASE AND ITS CAUSES*** + + +E-text prepared by Robert Shimmin, Carol David, Joshua Hutchinson, and the +Project Gutenberg Online Distributed Proofreading Team + + + +Note: Project Gutenberg also has an HTML version of this + file which includes the original illustrations. + See 15283-h.htm or 15283-h.zip: + (https://www.gutenberg.org/dirs/1/5/2/8/15283/15283-h/15283-h.htm) + or + (https://www.gutenberg.org/dirs/1/5/2/8/15283/15283-h.zip) + + + + + +DISEASE AND ITS CAUSES + +by + +W. T. COUNCILMAN, A.M., M.D., LL.D. +Professor of Pathology, Harvard University + +New York +Henry Holt and Company +London +Williams and Norgate +The University Press, Cambridge, U.S.A. + +1913 + + + + + + + +PREFACE + +In this little volume the author has endeavored to portray disease as +life under conditions which differ from the usual. Life embraces much +that is unknown and in so far as disease is a condition of living +things it too presents many problems which are insoluble with our +present knowledge. Fifty years ago the extent of the unknown, and at +that time insoluble questions of disease, was much greater than at +present, and the problems now are in many ways different from those in +the past. No attempt has been made to simplify the subject by the +presentation of theories as facts. + +The limitation as to space has prevented as full a consideration of +the subject as would be desirable for clearness, but a fair division +into the general and concrete phases of disease has been attempted. +Necessarily most attention has been given to the infectious diseases +and their causes. This not only because these diseases are the most +important but they are also the best known and give the simplest +illustrations. The space given to the infectious diseases has allowed +a merely cursory description of the organic diseases and such subjects +as insanity and heredity. Of the organic diseases most space has been +devoted to disease of the heart. There is slight consideration of the +environment and social conditions as causes of disease. + +Very few authors are mentioned in the text and no bibliography is +given. There is lack of literature dealing with the general aspects of +disease; the book moreover is not written for physicians, and the list +of investigators from whose work the knowledge of disease has been +derived would be too long to cite. + +It has been assumed that the reader has some familiarity with +elementary anatomy and physiology, and these subjects have been +considered only as much as is necessary to set the scene for the +drama. I am indebted to my friend, Mr. W. R. Thayer, for patiently +enduring the reading of the manuscript and for many suggestions as to +phrasing. + + + + +CONTENTS + + +CHAPTER PAGE + +CHAPTER I + +DEFINITION OF DISEASE.--CHARACTERISTICS OF LIVING MATTER.--CELLS AS +THE LIVING UNITS.--AMOEBA AS TYPE OF A UNICELLULAR ANIMAL.--THE +RELATION OF LIVING MATTER TO ENVIRONMENT.--CAPACITY OF ADAPTATION TO +ENVIRONMENT SHOWN BY LIVING MATTER.--INDIVIDUALITY OF LIVING +MATTER.--THE CAUSES OF DISEASE EXTRINSIC.--THE RELATION OF THE HUMAN +BODY TO THE ENVIRONMENT.--THE SURFACES OF THE BODY.--THE INCREASE OF +SURFACE BY GLAND FORMATION.--THE REAL INTERIOR OF THE BODY REPRESENTED +BY THE VARIOUS STRUCTURES PLACED BETWEEN THE SURFACES.--THE FLUIDS OF +THE BODY.--THE NERVOUS SYSTEM.--THE HEART AND BLOOD-VESSELS.--THE +CELLS OF THE BLOOD.--THE DUCTLESS GLANDS 9 + +CHAPTER II + +NO SHARP LINE OF DEMARCATION BETWEEN HEALTH AND DISEASE.--THE +FUNCTIONAL NUTRITIVE AND FORMATIVE ACTIVITIES OF CELLS.--DESTRUCTION +AND REPAIR CONSTANT PROCESSES IN LIVING MATTER.--INJURIES TO THE +BODY.--THE EFFECT OF HEAT.--THE ACTION OF POISONS.--THE LESIONS OF +DISEASE.--REPAIR.--THE LAWS GOVERNING REPAIR.--RELATION OF REPAIR TO +COMPLEXITY OF STRUCTURE AND AGE.--THE RESERVE FORCE OF THE +BODY.--COMPENSATORY PROCESSES IN THE BODY.--OLD AGE.--THE DIMINUTION +OF RESISTANCE TO THE EFFECTS OF THE ENVIRONMENT A PROMINENT FACTOR IN +OLD AGE.--DEATH.--HOW BROUGHT ABOUT.--CHANGES IN THE BODY AFTER +DEATH.--THE RECOGNITION OF DEATH 40 + +CHAPTER III + +THE GROWTH OF THE BODY.--GROWTH MORE RAPID IN EMBRYONIC PERIOD.--THE +COOeRDINATION AND REGULATION OF GROWTH.--TUMORS.--THE GROWTH OF TUMORS +COMPARED WITH NORMAL GROWTH.--SIZE. SHAPE AND STRUCTURE OF +TUMORS.--THE GROWTH CAPACITY OF TUMORS AS SHOWN BY THE INOCULATION OF +TUMORS OF MICE.--BENIGN AND MALIGNANT TUMORS.--EFFECT OF +INHERITANCE.--ARE TUMORS BECOMING MORE FREQUENT?--THE EFFECT PRODUCED +BY A TUMOR ON THE INDIVIDUAL WHO BEARS IT.--RELATION OF TUMORS TO AGE +AND SEX.--THEORIES AS TO THE CAUSE OF TUMORS.--THE PARASITIC +THEORY.--THE TRAUMATIC THEORY.--THE EMBRYONIC THEORY.--THE IMPORTANCE OF +THE EARLY RECOGNITION AND REMOVAL OF TUMORS 62 + +CHAPTER IV + +THE REACTIONS OF THE TISSUES OF THE BODY TO INJURIES.--INFLAMMATION.-- +THE CHANGES IN THE BLOOD IN THIS.--THE LMIGRATION OF THE CORPUSCLES OF +THE BLOOD.--THE EVIDENT CHANGES IN THE INJURED PART AND THE MANNER IN +WHICH THESE ARE PRODUCED.--HEAT REDNESS SWELLING AND PAIN.--THE +PRODUCTION OF BLISTERS BY SUNBURN.--THE CHANGES IN THE CELLS OF AN +INJURED PART.--THE CELLS WHICH MIGRATE FROM THE BLOOD VESSELS ACT AS +PHAGOCYTES.--THE MACROPHAGES.--THE MICROPHAGES.--CHEMOTROPISM.--THE +HEALING OF INFLAMMATION.--THE REMOVAL OF THE CAUSE.--CELL REPAIR AND NEW +FORMATION.--NEW FORMATION OF BLOOD VESSELS.--ACUTE AND CHRONIC +INFLAMMATION.--THE APPARENTLY PURPOSEFUL CHARACTER OF THE CHANGES IN +INFLAMMATION 79 + +CHAPTER V + +INFECTIOUS DISEASES.--THE HISTORICAL IMPORTANCE OF EPIDEMICS OF +DISEASE.--THE LOSSES IN BATTLE CONTRASTED WITH THE LOSSES IN ARMIES +PRODUCED BY INFECTIOUS DISEASES.--THE DEVELOPMENT OF KNOWLEDGE OF +EPIDEMICS.--THE VIEWS OF HIPPOCRATES AND ARISTOTLE.--SPORADIC AND +EPIDEMIC DISEASES.--THE THEORY OF THE EPIDEMIC CONSTITUTION.--THEORY +THAT THE CONTAGIOUS MATERIAL IS LIVING.--THE DISCOVERY OF BACTERIA BY +LOEWENHOECK IN 1675.--THE RELATION OF CONTAGION TO THE THEORY OF +SPONTANEOUS GENERATION.--NEEDHAM AND SPALLANZANI.--THE DISCOVERY OF THE +COMPOUND MICROSCOPE IN 1605.--THE PROOF THAT A LIVING ORGANISM IS THE +CAUSE OF A DISEASE.--ANTHRAX.--THE DISCOVERY OF THE ANTHRAX BACILLUS IN +1851.--THE CULTIVATION OF THE BACILLUS BY KOCH.--THE MODE OF +INFECTION.--THE WORK OF PASTEUR ON ANTHRAX.--THE IMPORTANCE OF THE +DISEASE 97 + +CHAPTER VI + +CLASSIFICATION OF THE ORGANISMS WHICH CAUSE DISEASE.--BACTERIA SIZE +SHAPE STRUCTURE CAPACITY FOR GROWTH MULTIPLICATION AND SPORE +INFORMATION.--THE ARTIFICIAL CULTIVATION OF BACTERIA.--THE IMPORTANCE +OF BACTERIA IN NATURE.--VARIATIONS IN BACTERIA.--SAPROPHYTIC AND +PARASITIC FORMS.--PROTOZOA.--STRUCTURE MORE COMPLICATED THAN THAT OF +BACTERIA.--DISTRIBUTION IN NATURE.--GROWTH AND +MULTIPLICATION.--CONJUGATION AND SEXUAL REPRODUCTION.--SPORE +FORMATION.--THE NECESSITY FOR A FLUID ENVIRONMENT.--THE FOOD OF +PROTOZOA.--PARASITISM.--THE ULTRA MICROSCOPIC OR FILTERABLE +ORGANISMS.--THE LIMITATION OF THE MICROSCOPIC.--PORCELAIN FILTERS TO +SEPARATE ORGANISMS FROM A FLUID.--FOOT AND MOUTH DISEASE PRODUCED BY AN +ULTRA MICROSCOPIC ORGANISM.--OTHER DISEASES SO PRODUCED.--DO NEW +DISEASES APPEAR? 116 + +CHAPTER VII + +THE NATURE OF INFECTION.--THE INVASION OF THE BODY FROM ITS +SURFACES.--THE PROTECTION OF THESE SURFACES.--CAN BACTERIA PASS THROUGH +AN UNINJURED SURFACE?.--INFECTION FROM WOUNDS.--THE WOUNDS IN MODERN +WARFARE LESS PRONE TO INFECTION.--THE RELATION OF TETANUS TO WOUNDS +CAUSED BY THE TOY PISTOL.--THE PRIMARY FOCUS OR ATRIUM OF +INFECTION.--THE DISSEMINATION OF BACTERIA IN THE BODY.--THE DIFFERENT +DEGREES OF RESISTANCE TO BACTERIA SHOWN BY THE VARIOUS ORGANS.--MODE OF +ACTION OF BACTERIA.--TOXIN PRODUCTION.--THE RESISTANCE OF THE BODY TO +BACTERIA.--CONFLICT BETWEEN PARASITE AND HOST.--ON BOTH SIDES MEANS OF +OFFENSE AND DEFENSE.--PHAGOCYTOSIS.--THE DESTRUCTION OF BACTERIA BY THE +BLOOD.--THE TOXIC BACTERIAL DISEASES.--TOXIN AND ANTITOXIN.--IMMUNITY.-- +THE THEORY OF EHRLICH 135 + +CHAPTER VIII + +SECONDARY TERMINAL AND MIXED INFECTIONS.--THE EXTENSION OF INFECTION IN +THE INDIVIDUAL.--TUBERCULOSIS.--THE TUBERCLE BACILLUS.--FREQUENCY OF THE +DISEASE.--THE PRIMARY FOCI.--THE EXTENSION OF BACILLI.--THE DISCHARGE OF +BACILLI FROM THE BODY.--INFLUENCE OF THE SEAT OF DISEASE ON THE +DISCHARGE OF BACILLI.--THE INTESTINAL DISEASES.--MODES OF +INFECTION.--INFECTION BY SPUTUM SPRAY.--INFECTION OF WATER +SUPPLIES.--EXTENSION OF INFECTION BY INSECTS.--TRYPANASOME +DISEASES.--SLEEPING SICKNESS.--MALARIA.--THE PART PLAYED BY +MOSQUITOES.--PARASITISM IN THE MOSQUITO.--INFECTION AS INFLUENCED BY +HABITS AND CUSTOMS.--HOOKWORM DISEASE.--INTERRELATION BETWEEN HUMAN AND +ANIMAL DISEASES.--PLAGUE.--PART PLAYED RATS IN TRANSMISSION.--THE PRESENT +EPIDEMIC OF PLAGUE 159 + +CHAPTER IX + +DISEASE CARRIERS.--THE RELATION BETWEEN SPORADIC CASES OF INFECTIOUS +DISEASE AND EPIDEMICS.--SMALLPOX.--CEREBROSPINAL +MENINGITIS.--POLYOMYELITIS.--VARIATION IN THE SUSCEPTIBILITY OF +INDIVIDUALS.--CONDITIONS WHICH MAY INFLUENCE SUSCEPTIBILITY.--RACIAL +SUSCEPTIBILITY.--INFLUENCE OF AGE AND SEX.--OCCUPATION AND +ENVIRONMENT.--THE AGE PERIOD OF INFECTIOUS DISEASES 185 + +CHAPTER X + +INHERITANCE AS A FACTOR IN DISEASE.--THE PROCESS OF CELL +MULTIPLICATION.--THE SEXUAL CELLS DIFFER FROM THE OTHER CELLS OF THE +BODY.--INFECTION OF THE OVUM.--INTRAUTERINE INFECTION.--THE PLACENTA AS A +BARRIER TO INFECTION.--VARIATIONS AND MUTATIONS.--THE INHERITANCE OF +SUSCEPTIBILITY TO DISEASE.--THE INFLUENCE OF ALCOHOLISM IN THE PARENTS +ON THE DESCENDANTS.--THE HEREDITY OF NERVOUS DISEASES.--TRANSMISSION OF +DISEASE BY THE FEMALE ONLY.--HEMOPHILIA.--THE INHERITANCE OF +MALFORMATIONS.--THE CAUSES OF MALFORMATIONS.--MATERNAL IMPRESSIONS HAVE +NO INFLUENCE.--EUGENICS 197 + +CHAPTER XI + +CHRONIC DISEASES.--DISEASE OF THE HEART AS AN EXAMPLE.--THE STRUCTURE +AND FUNCTION OF THE HEART.--THE ACTION OF THE VALVES.--THE PRODUCTION +OF HEART DISEASE BY INFECTION.--THE CONDITIONS PRODUCED IN THE +VALVES.--THE MANNER IN WHICH DISEASE OF THE VALVES INTERFERES WITH +THEIR FUNCTION,--THE COMPENSATION OF INJURY BY INCREASED ACTION OF +HEART.--THE ENLARGEMENT OF THE HEART.--THE RESULT OF IMPERFECT WORK OF +THE HEART.--VENOUS CONGESTION.--DROPSY.--CHRONIC DISEASE OF THE +NERVOUS SYSTEM.--INSANITY.--RELATION BETWEEN INSANITY AND +CRIMINALITY.--ALCOHOLISM AND SYPHILIS FREQUENT CAUSES OF +INSANITY.--THE DIRECT AND INDIRECT CAUSES OF NERVOUS DISEASES.--THE +RELATION BETWEEN SOCIAL LIFE AND NERVOUS DISEASES.--FUNCTIONAL AND +ORGANIC DISEASE.--NEURASTHENIA 219 + +CHAPTER XII + +THE RAPID DEVELOPMENT OF MEDICINE IN THE LAST FIFTY YEARS.--THE +INFLUENCE OF DARWIN.--PREVENTIVE MEDICINE.--THE DISSEMINATION OF +MEDICAL KNOWLEDGE.--THE DEVELOPMENT OF CONDITIONS IN RECENT YEARS +WHICH ACT AS FACTORS OF DISEASE.--FACTORY LIFE.--URBAN LIFE.--THE +INCREASE OF COMMUNICATION BETWEEN PEOPLES.--THE INTRODUCTION OF PLANT +PARASITES.--THE INCREASE IN ASYLUM LIFE.--INFANT MORTALITY.--WEALTH +AND POVERTY AS FACTORS IN DISEASE 241 + +GLOSSARY 250 + +INDEX 252 + + + + + +DISEASE AND ITS CAUSES + + + + +CHAPTER I + +DEFINITION OF DISEASE.--CHARACTERISTICS OF LIVING MATTER.--CELLS AS +THE LIVING UNITS.--AMOEBA AS TYPE OF A UNICELLULAR ANIMAL.--THE +RELATION OF LIVING MATTER TO THE ENVIRONMENT.--CAPACITY OF ADAPTATION +TO THE ENVIRONMENT SHOWN BY LIVING MATTER--INDIVIDUALITY OF LIVING +MATTER.--THE CAUSES OF DISEASE.--EXTRINSIC.--THE RELATION OF THE HUMAN +BODY TO THE ENVIRONMENT.--THE SURFACES OF THE BODY.--THE INCREASE OF +SURFACE BY GLAND FORMATION.--THE REAL INTERIOR OF THE BODY REPRESENTED +BY THE VARIOUS STRUCTURES PLACED BETWEEN THE SURFACES.--THE FLUIDS OF +THE BODY.--THE NERVOUS SYSTEM.--THE HEART AND BLOOD-VESSELS.--THE +CELLS OF THE BLOOD.--THE DUCTLESS GLANDS. + + +There is great difficulty, in the case of a subject so large and +complex as is disease, in giving a definition which will be accurate +and comprehensive. Disease may be defined as "A change produced in +living things in consequence of which they are no longer in harmony +with their environment." It is evident that this conception of disease +is inseparable from the idea of life, since only a living thing can +become diseased. In any dead body there has been a preexisting disease +or injury, and, in consequence of the change produced, that particular +form of activity which constitutes life has ceased. Changes such as +putrefaction take place in the dead body, but they are changes which +would take place in any mass similarly constituted, and are not +influenced by the fact that the mass was once living. Disease may also +be thought of as the negation of the normal. There is, however, in +living things no definite type for the normal. An ideal normal type +may be constructed by taking the average of a large number of +individuals; but any single individual of the group will, to a greater +or less extent, depart from it. No two individuals have been found in +whom all the Bertillon measurements agree. Disease has reference to +the individual; conditions which in one individual would be regarded +as disease need not be so regarded in another. Comparisons between +health and disease, the normal and the abnormal, must be made not +between the ideal normal and abnormal, but between what constitutes +the normal or usual and the abnormal in a particular individual. + +The conception of disease is so inseparably associated with that of +life that a brief review of the structure and properties of living +things is necessary for the comprehension of the definition which has +been given. Living matter is subject to the laws which govern matter, +and like matter of any other sort it is composed of atoms and +molecules. There is no force inherent in living matter, no vital force +independent of and differing from the cosmic forces; the energy which +living matter gives off is counterbalanced by the energy which it +receives. It undergoes constant change, and there is constant +interchange with the environment. The molecules which compose it are +constantly undergoing change in their number, kind and arrangement. +Atom groups as decomposition products are constantly given off from +it, and in return it receives from without other atom groups with +which it regenerates its substance or increases in amount. All +definitions of life convey this idea of activity. Herbert Spencer +says, "Life is the continuous adjustment of internal relations to +external conditions." The molecules of the substances forming the +living material are large, complex and unstable, and as such they +constantly tend to pass from the complex to the simple, from unstable +to stable equilibrium. The elementary substances which form living +material are known, but it has hitherto not been found possible +artificially so to combine these substances that the resulting mass +will exhibit those activities which we call the phenomena of life. The +distinction between living and nonliving matter is manifest only when +the sum of the activities of the living matter is considered; any +single phenomenon of the living may appear also in the non-living +material. Probably the most distinguishing criterion of living matter +is found in its individuality, which undoubtedly depends upon +differences in structure, whether physical or chemical, between the +different units. + +Certain conditions are essential for the continued existence of living +matter. It must be surrounded by a fluid or semi-fluid medium in order +that there may be easy interchange with the environment. It must +constantly receive from the outside a supply of energy in the form of +food, and substances formed as the result of the intracellular +chemical activity must be removed. In the case of many animals it +seems as though the necessity of a fluid environment for living matter +did not apply, for the superficial cells of the skin have no fluid +around them; these cells, however, are dead, and serve merely a +mechanical or protective purpose. All the living cells of the skin and +all the cells beneath this have fluid around them. + +Living matter occurs always in the form of small masses called +"cells," which are the living units. The cells vary in form, structure +and size, some being so large that they can be seen with the naked +eye, while others are so small that they cannot be distinctly seen +with the highest power of the microscope. The living thing or organism +may be composed of a single cell or, in the case of the higher animals +and plants, may be formed of great numbers of cells, those of a +similar character being combined in masses to form organs such as the +liver and brain. + +In each cell there is a differentiated area constituting a special +structure, the nucleus, which contains a peculiar material called +"chromatin." The nucleus has chiefly to do with the multiplication of +the cell and contains the factors which determine heredity. The mass +outside of the nucleus is termed "cytoplasm," and this may be +homogeneous in appearance or may contain granules. On the outside +there is a more or less definite cell membrane. It is generally +believed that the cell material has a semi-fluid or gelatinous +consistency and is contained within an intracellular meshwork. It is +an extraordinarily complex mass, whether regarded from a chemical or +physical point of view. (Fig. 1.) + +[Illustration: FIG. 1.--DIAGRAM OF CELL. 1. Cell membrane. 2. Cell +substance or cytoplasm. 3. Nucleus. 4. Nuclear membrane. +5. Nucleolus.] + +A simple conception of health and disease can be arrived at by the +study of these conditions in a unicellular animal directly under a +microscope, the animal being placed on a glass slide. For this purpose +a small organism called "Amoeba" (Fig. 2), which is commonly present +in freshwater ponds, may be used. This appears as a small mass, +seemingly of gelatinous consistency with a clear outline, the exterior +part homogeneous, the interior granular. The nucleus, which is seen +with difficulty, appears as a small vesicle in the interior. Many +amoebae show also in the interior a small clear space, the contractile +vesicle which alternately contracts and expands, through which action +the movement of the intracellular fluid is facilitated and waste +products removed. The interior granules often change their position, +showing that there is motion within the mass. The amoeba slowly moves +along the surface of the glass by the extension of blunt processes +formed from the clear outer portion which adhere to the surface and +into which the interior granular mass flows. This movement does not +take place by chance, but in definite directions, and may be +influenced. The amoeba will move towards certain substances which may +be placed in the fluid around it and away from others. In the water in +which the amoebae live there are usually other organisms, particularly +bacteria, on which they feed. When such a bacterium comes in contact +with an amoeba, it is taken into its body by becoming enclosed in +processes which the amoeba sends out. The enclosed organism then lies +in a small clear space in the amoeba, surrounded by fluid which has +been shown to differ in its chemical reaction from the general fluid +of the interior. This clear space, which may form at any point in the +body, corresponds to a stomach in a higher animal and the fluid within +it to the digestive fluid or gastric juice. After a time the enclosed +organism disappears, it has undergone solution and is assimilated; +that is, the substances of which its body was composed have been +broken up, the molecules rearranged, and a part has been converted +into the substance of the amoeba. If minute insoluble substances, such +as particles of carmine, are placed in the water, these may also be +taken up by the amoeba; but they undergo no change, and after a time +they are cast out. Under the microscope only the gross vital +phenomena, motion of the mass, motion within the mass, the reception +and disintegration of food particles, and the discharge of inert +substances can be observed. The varied and active chemical changes +which are taking place cannot be observed. + +[Illustration: FIG. 2.--AMOEBA. 1. Nucleus. 2. Contractile vesicle. +3. Nutritive vacuole containing a bacillus.] + +Up to the present it has been assumed that the environment of the +amoeba is that to which it has become adapted and which is favorable +to its existence. Under these conditions its structure conforms to the +type of the species, as do also the phenomena which it exhibits, and +it can assimilate food, grow and multiply. If, during the observation, +a small crystal of salt be placed in the fluid, changes almost +instantly take place. Motion ceases, the amoebae appear to shrink into +smaller compass, and they become more granular and opaque. If they +remain a sufficiently long time in this fluid, they do not regain +their usual condition when placed again in fresh water. None of the +phenomena which characterized the living amoebae appear: we say they +are dead. After a time they begin to disintegrate, and the bacteria +contained in the water and on which the amoebae fed now invade their +tissue and assist in the disintegration. By varying the duration of +the exposure to the salt water or the amount of salt added, a point +can be reached where some, but not all, of the amoebae are destroyed. +Whether few or many survive depends upon the degree of injury +produced. Much the same phenomena can be produced by gradually heating +the water in which the amoebae are contained. It is even possible +gradually to accustom such small organisms to an environment which +would destroy them if suddenly subjected to it, but in the process of +adaptation many individuals will have perished. + +It is evident from such an experiment that when a living organism is +subject to an environment to which it has not become adapted and which +is unfavorable, such alterations in its structure may be produced that +it is incapable of living even when it is again returned to the +conditions natural to it. Such alterations of structure or injuries +are called the _lesions_ of disease. We have seen that in certain +individuals the injury was sufficient to inhibit for a time only the +usual manifestations of life; these returned when the organism was +removed from the unfavorable conditions, and with this or preceding it +the organisms, if visibly altered, regained the usual form and +structure. We may regard this as disease and recovery. In the disease +there is both the injury or lesion and the derangement of vital +activity dependent upon this. The cause of the disease acted on the +organism from without, it was external to it. Whether the injurious +external conditions act as in this case by a change in the surrounding +osmotic pressure, or by the destruction of ferments within the cell, +or by the introduction into the cell of substances which form stable +chemical union with certain of its constituents, and thus prevent +chemical processes taking place which are necessary for life, the +result is the same. + +The experiments with the amoebae show also two of the most striking +characteristics of living matter. 1. It is _adaptable_. Under the +influence of unusual conditions, alterations in structure and possibly +in substance, may take place, in consequence of which the organisms +under such external conditions may still exhibit the usual phenomena. +The organism cannot adapt itself to such changes without undergoing +change in structure, although there may be no evidence of such changes +visible. This alteration of structure does not constitute a disease, +provided the harmonious relation of the organism with the environment +be not impaired. An individual without a liver should not be regarded +as diseased, provided there can be such an internal adjustment that +all of the vital phenomena could go on in the usual manner without the +aid of this useful and frequently maligned organ. 2. It is +_individual_. In the varying degrees of exposure to unfavorable +conditions of a more serious nature some, but not all, of the +organisms are destroyed; in the slight exposure, few; in the longer, +many. Unfavorable conditions which will destroy all individuals of a +species exposed to them must be extremely rare.[1] There is no such +individuality in non-living things. In a mass of sugar grains each +grain shows just the same characteristics and reacts in exactly the +same way as all the other grains of the mass. Individuality, however +expressed, is due to structural variation. It is almost impossible to +conceive in the enormous complexity of living things that any two +individuals, whether they be single cells or whether they be formed of +cell masses, can be exactly the same. It is not necessary to assume in +such individual differences that there be any variation in the amount +and character of the component elements, but the individuality may be +due to differences in the atomic or molecular arrangements. There are +two forms of tartaric-acid crystals of precisely the same chemical +formula, one of which reflects polarized light to the left, and the +other to the right. All the left-sided crystals and all the +right-sided are, however, precisely the same. The number of possible +variations in the chemical structure of a substance so complex as is +protoplasm is inconceivable. + +In no way is the individuality of living matter more strongly +expressed than in the resistance to disease. The variation in the +degree of resistance to an unfavorable environment is seen in every +tale of shipwreck and exposure. In the most extensive epidemics +certain individuals are spared; but here care must be exercised in +interpreting the immunity, for there must be differences in the degree +of exposure to the cause of the epidemic. It would not do to interpret +the immunity to bullets in battle as due to any individual +peculiarity, save possibly a tendency in certain individuals to remove +the body from the vicinity of the bullets; in battle and in epidemics +the factors of chance and of prudence enter. No other living organism +is so resistant to changes in environment as is man, and to this +resistance he owes his supremacy. By means of his intelligence he can +change the environment. He is able to resist the action of cold by +means of houses, fire and clothing; without such power of intelligent +creation of the immediate environment the climatic area in which man +could live would be very narrow. Just as disease can be acquired by an +unfavorable environment, man can so adjust his environment to an +injury that harmony will result in spite of the injury. The +environment which is necessary to compensate for an injury may become +very narrow. For an individual with a badly working heart more and +more restriction of the free life is necessary, until finally the only +environment in which life is even tolerably harmonious is between +blankets and within the walls of a room. + +The various conditions which may act on an organism producing the +changes which are necessary for disease are manifold. Lack of +resistance to injury, incapacity for adaptation, whether it be due to +a congenital defect or to an acquired condition, is not in itself a +disease, but the disease is produced by the action on such an +individual of external conditions which may be nothing more than those +to which the individuals of the species are constantly subject and +which produce no harm. + +[Illustration: FIG. 3.--A SECTION OF THE SKIN. 1. A hair. Notice there +is a deep depression of the surface to form a small bulb from which +the hair grows. 2. The superficial or horny layer of the skin; the +cells here are joined to form a dense, smooth, compact layer +impervious to moisture. 3. The lower layer of cells. In this layer new +cells are continually being formed to supply those which as thin +scales are cast off from the surface. 4. Section of a small vein. 9. +Section of an artery. 8. Section of a lymphatic. The magnification is +too low to show the smaller blood vessels. 5. One of the glands +alongside of the hair which furnishes an oily secretion. 6. A sweat +gland. 7. The fat of the skin. Notice that hair, hair glands and sweat +glands are continuous with the surface and represent a downward +extension of this. All the tissue below 2 and 3 is the corium from +which leather is made.] + +[Illustration: FIG. 4.--DIAGRAMMATIC SECTION OF A SURFACE SHOWING THE +RELATION OF GLANDS TO THE SURFACE. (_a_) Simple or tubular gland, +(_b_) compound or racemose gland.] + +All of the causes of disease act on the body from without, and it is +important to understand the relations which the body of a highly +developed organism such as man has with the world external to him. +This relation is effected by means of the various surfaces of the +body. On the outside is the skin [Fig. 3], which surface is many times +increased by the existence of glands and such appendages to the skin +as the hair and nails. A gland, however complicated its structure, is +nothing more than an extension of the surface into the tissue beneath +[Fig. 4]. In the course of embryonic development all glands are formed +by an ingrowth of the surface. The cells which line the gland surface +undergo a differentiation in structure which enables them to perform +certain definite functions, to take up substances from the same source +of supply and transform them. The largest gland on the external +surface of the body is the mammary gland [Fig. 5] in which milk is +produced; there are two million small, tubular glands, the sweat +glands, which produce a watery fluid which serves the purpose of +cooling the body by evaporation; there are glands at the openings of +the hairs which produce a fatty secretion which lubricates the hair +and prevents drying, and many others. + +[Illustration: FIG. 5.--A SECTION OF THE MAMMARY GLAND. (_a_) The +ducts of the gland, by which the milk secreted by the cells which line +all the small openings, is conveyed to the nipple. All these openings +are continuous with the surface of the skin. On each side of the large +ducts is a vein filled with blood corpuscles.] + +[Illustration: FIG. 6.--PHOTOGRAPH OF A SECTION OF THE LUNG OF A MOUSE. +_x x_ are the air tubes or bronchi which communicate with all of +the small spaces. On the walls of the partitions there is a close +network of blood vessels which are separated from the air in the +spaces by a thin membrane.] + +The external surface passes into the interior of the body forming two +surfaces, one of which, the intestinal canal, communicates in two +places, at the mouth and anus, with the external surface; and the +other, the genito-urinary surface, which communicates with the +external surface at one place only. The surface of the intestinal +canal is much greater in extent than the surface on the exterior, and +finds enormous extensions in the lungs and in the great glands such as +the liver and pancreas, which communicate with it by means of their +ducts. The extent of surface within the lungs is estimated at +ninety-eight square yards, which is due to the extensive infoldings of +the surface [Fig 6], just as a large surface of thin cloth can, by +folding, be compressed into a small space. The intestinal canal from +the mouth to the anus is thirty feet long, the circumference varies +greatly, but an average circumference of three inches may safely be +assumed, which would give between seven and eight square feet of +surface, this being many times multiplied by adding the surfaces of +the glands which are connected with it. A diagram of the microscopic +structure of the intestinal wall shows how little appreciation of the +extent of surface the examination with the naked eye gives [Fig. 7]. +By means of the intestinal canal food or substances necessary to +provide the energy which the living tissue transforms are introduced. +This food is liquefied and so altered by the action of the various +fluids formed in the glands of the intestine and poured out on the +surface, that it can pass into the interior of the body and become +available for the living cells. Various food residues representing +either excess of material or material incapable of digestion remain in +the intestine, and after undergoing various changes, putrefactive in +character, pass from the anus as feces. + +[Illustration: FIG. 7.--A SECTION OF THE SMALL INTESTINE TO SHOW THE +LARGE EXTENT OF SURFACE. (_a_) Internal surface. The small finger-like +projections are the villi, and between these are small depressions +forming tubular glands.] + +By means of the lungs, which represent a part of the surface, the +oxygen of the air, which is indispensable for the life of the cells, +is taken into the body and carbonic acid removed. The interchange of +gases is effected by the blood, which, enclosed in innumerable, small, +thin-walled tubes, almost covers the surface, and comes in contact +with the air within the lungs, taking from it oxygen and giving to it +carbonic acid. + +The genito-urinary surface is the smallest of the surfaces. In the +male (Fig. 8,--27, 28, 30) this communicates with the general external +surface by the small opening at the extremity of the penis, and in the +female by the opening into the vagina. In its entirety it consists in +a surface of wide extent, comprising in the male the urethra, a long +canal which opens into the bladder, and is continuous with ducts that +lead into the genital glands or testicles. The internal surface of the +bladder is extended by means of two long tubes, the ureters, into the +kidneys, and receives the fluid formed in these organs. In the female +(Fig 9) there is a shallow external orifice which is continued into +the bladder by a short canal, the urethra, the remaining urinary +surface being the same as in the male; the external opening also is +extended into the short, wide tube of the vagina, which is continuous +with the canal of the uterus. This canal is continued on both sides +into the Fallopian tubes or oviducts. There is thus in the female a +more complete separation of the urinary and the genital surfaces than +in the male. Practically all of the waste material of the body which +results from cell activity and is passed from the cells into the fluid +about them is brought by the blood to the kidneys, and removed by +these from the blood, leaving the body as urine. + + +[Illustration: FIG. 8.--A LONGITUDINAL SECTION THROUGH THE MIDDLE OF +THE BODY SHOWING THE EXTERNAL AND INTERNAL SURFACES AND THE ORGANS. + +1. The skull. +2. The brain, showing the convolutions of the gray exterior in which + the nerve cells are most numerous. +3. The white matter in the interior of the brain formed of nerve + fibres which connect the various parts of this. +4. The small brain or cerebellum. +5. The interior of the nose. Notice the nearness of the upper part of + this cavity to the brain. +6. The hard or bony palate forming the roof of the mouth. +7. The soft palate which hangs as a curtain between the mouth and the + pharynx. +8. The mouth cavity. +9. The tongue. +10. The beginning of the gullet or oesophagus. +11. The larynx. +12. The windpipe or trachea. +13. The oesophagus. +14. The thyroid gland. +15. The thymus gland or sweetbread. +16. The large vein, vena cava, which conveys the blood from the brain + and upper body into the heart. +17-25. Lymph nodes; 17, of the neck; 25, of the abdomen. +18. Cross section of the arch of the aorta or main artery of the body + after it leaves the heart. +19. The sternum or breast bone. +20. The cavity of the heart. +21. The liver. +22. The descending aorta at the back of the abdominal cavity. +23. The pancreas. +24. The stomach. +26. Cross section of the intestines. +27. The urinary bladder. +28. The entrance into this of the ureter or canal from the kidney. +29. Cross sections of the pubic bone. +30. The canal of the urethra leading into the bladder. +31. The penis. +32. The spinal cord. +33. The bones composing the spinal column. +34. The sacrum. The space between this and No. 29 is the pelvis. +35. The coccyx or extremity of the back bone. +36. The rectum. +37. The testicles.] + +Between these various surfaces is the real interior of the body, in +which there are many sorts of living tissues,[2] each, of which, in +addition to maintaining itself, has some function necessary for the +maintenance of the body as a whole. Many of these tissues have for +their main purpose the adjustment and cooerdination of the activities +of the different organs to the needs of the organism as a whole. The +activity of certain of the organs is essential for the maintenance of +life; without others life can exist for a time only; and others, such +as the genital glands, while essential for the preservation of the +life of the species, are not essential for the individual. There is a +large amount of reciprocity among the tissues; in the case of paired +organs the loss of one can be made good by increased activity of the +remaining, and certain of the organs are so nearly alike in function +that a loss can be compensated for by an increase or modification of +the function of a nearly related organ. The various internal parts are +connected by means of a close meshwork of interlacing fibrils, the +connective tissue, support and strength being given by the various +bones. Everywhere enclosing all living cells and penetrating into the +densest of the tissues there is fluid. We may even consider the body +between the surfaces as a bag filled with fluid into which the various +cells and structures are packed. + +[Illustration: FIG. 9.--A LONGITUDINAL SECTION THROUGH THE FEMALE +PELVIS. + +1. The Fallopian tube which forms the connection between +the ovary and the uterus. +2. The ovary. +3. The body of the uterus. +4. The uterine canal. +5. The urinary bladder represented as empty. +6. The entrance of the ureter. +7. The pubic bone. +8. The urethra. +9. The vagina. +10. The common external opening or vulva. +11. The rectum and anus.] + +[Illustration: FIG. 10.--THE LUNGS AND WINDPIPE. Parts of the lungs +have been removed to show the branching of the air tubes or bronchi +which pass into them. All the tubes and the surfaces of the lungs +communicate with the inner surface of the body through the larynx.] + +The nervous system (Fig. 8) represents one of the most important of +the enclosed organs. It serves an important function, not only in +regulating and cooerdinating all functions, but by means of the special +senses which are a part of it, the relations of the organism as a +whole with the environment are adjusted. It consists of a large +central mass, the brain and spinal cord, which is formed in the embryo +by an infolding of the external surface, much in the same way that a +gland is formed; but the connection with the surface is lost in +further development and it becomes completely enclosed. Connected with +the central nervous mass, forming really a part of it and developing +from it, are the nerves, which appear as white fibrous cords and after +dividing and subdividing, are as extremely fine microscopic filaments +distributed to all parts of the body. By means of the nerves all +impressions are conveyed to the brain and spinal cord; all impulses +from this, whether conscious or unconscious, are conveyed to the +muscles and other parts. The brain is the sole organ of psychical +life; by means of its activity the impressions of the external world +conveyed to it through the sense organs are converted into +consciousness. Whatever consciousness is, and on this much has been +written, it proceeds from or is associated with the activity of the +brain cells just as truly as the secretion of gastric juice is due to +the activity of the cells of the stomach. The activity of the nervous +system is essential for extra-uterine life; life ceases by the +cessation of circulation and respiration when either the whole or +certain small areas of its tissue are destroyed. In intra-uterine +life, with the narrow and unchanging environment of the fluid within +the uterine cavity which encloses the foetus, life is compatible with +the absence or rudimentary development of the nervous system. The +foetus in this condition may be otherwise well developed, and it would +be not a misuse of words to say that it was healthy, since it is +adjusted to and in harmony with its narrow environment, but it would +not be normal. The intra-uterine life of the unborn child, it must be +remembered, is carried out by the transmission of energy from the +mother to the foetus by means of the close relation between the +maternal and foetal circulation. It is only when the free existence +demands activities not necessary in intra-uterine life that existence +without a central nervous system becomes impossible. + +It is essential in so complicated a structure as the body that some +apparatus should exist to provide for the interchange of material. The +innumerable cell units of the body must have material to provide +energy, and useless material which results from their activity must be +removed. A household might be almost as much embarrassed by the +accumulation of garbage and ashes as by the absence of food and coal. +The food, which is taken into the alimentary canal and converted by +the digestive fluids into material more directly adapted to the uses +of cells, must be conveyed to them. A supply of oxygen is essential +for the life of the cells, and the supply which is given by +respiration must be carried from the lungs to every cell of the body. +All this is effected by the circulation of the blood, which takes +place in the system of branching closed tubes in which the blood +remains (Fig. 11). Certain of these tubes, the arteries, have strong +and elastic walls and serve to convey and distribute the blood to the +different organs and tissues. From the ultimate branches of the +arteries the blood passes into a close network of tubes, the +capillaries, which in enormous numbers are distributed in the tissues +and have walls so thin that they allow fluid and gaseous interchange +between their contents and the fluid around them to take place. The +blood from the capillaries is then collected into a series of tubes, +the veins, by which it is returned to the heart. This circulation is +maintained by means of a pumping organ or heart, which receives the +blood from the veins and by the contraction of its powerful walls +forces this into the arteries, the direction of flow being determined +as in a pump, by a system of valves. The waste products of cell life +pass from the cells into the fluid about them, and are in part +directly returned into the blood, but for the greater part pass into +it indirectly through another set of vessels, the lymphatics. These +are thin-walled tubes which originate in the tissues, and in which +there is a constant flow towards the heart, maintained by the constant +but varying pressure of the tissue around them, the direction of flow +being maintained by numerous valves. The colorless fluid within these +vessels is termed "lymph." At intervals along these tubes are small +structures termed the lymph nodes, which essentially are filters, and +strain out from the fluid substances which might work great injury if +they passed into the blood. Between the capillary vessels and the +lymphatics is the tissue fluid, in which all the exchange takes place. +It is constantly added to by the blood, and returns fluid to the blood +and lymph; it gives material to the cells and receives material from +them. + +[Illustration: FIG. 11.--A DIAGRAMMATIC VIEW OF THE BLOOD VESSELS. An +artery (_a_) opens into a system of capillaries, (_c_) and +after passing through these collects into a vein (_b_). Notice +that the capillaries connect with other vascular territories at +numerous points (_d_). If the artery (_a_) became closed the +capillaries which it supplies could be filled by blood coming from +other sources.] + +In addition to the strength and elasticity of the wall of the +arteries, which enables them to resist the pressure of the blood, they +have the power of varying their calibre by the contraction or +expansion of their muscular walls. Many of the organs of the body +function discontinuously, periods of activity alternating with +comparative repose; during the period of activity a greater blood +supply is demanded, and is furnished by relaxation of the muscle +fibres which allows the calibre to increase, and with this the blood +flow becomes greater in amount. Each part of the body regulates its +supply of blood, the regulation being effected by means of nerves +which control the tension of the muscle fibres. The circulation may be +compared with an irrigation system in which the water supply of each +particular field is regulated not by the engineer, but by an automatic +device connected with the growing crop and responding to its demands. + +[Illustration: FIG. 12.--THE VARIOUS CELLS IN THE BLOOD. (_a_) The red +blood cells, single and forming a roll by adhering to one another; +(_b_) different forms of the white blood cells; those marked "1" are +the most numerous and are phagocytic for bacteria.] + +The blood consists of a fluid, the blood plasma, in which numerous +cells are contained. The most numerous of these are small cup-shaped +cells which contain a substance called _haemoglobin_, to which the +red color of the blood is due. There are five million of these cells +in a cubic millimeter (a millimeter is .03937 of an inch), giving a +total number for the average adult of twenty-five trillion. The +surface area of all these, each being one thirty-three hundredth of an +inch in diameter, is about thirty-three hundred square yards. The +haemoglobin which they contain combines in the lungs with the oxygen in +the inspired air, and they give up this indispensable substance to the +cells everywhere in the body. There are also eight thousand leucocytes +or colorless cells in a cubic millimeter of blood, this giving a total +number of four billion in the average adult, and these vary in +character and in relative numbers (Fig. 12). The most numerous of +these are round and slightly larger than the red cells; they have a +nucleus of peculiar shape and contain granules of a definite +character. These cells serve an important part in infectious diseases +in devouring and destroying parasites. They have power of active +independent motion and somewhat resemble certain of the free living +unicellular organisms. The blood plasma, when taken from the vessels, +clots or passes from a fluid into a gelatinous or semi-solid +condition, which is due to the formation within it of a network of +fine threads termed fibrin. It is by means of the clotting of the +blood that the escape of blood from ruptured vessels is arrested. + +Several of the organs of the body, in addition to the formation of +secretions which are discharged on the surfaces by means of their +ducts, produce also substances which pass directly into the blood or +lymph, and have an influence in stimulating or otherwise regulating +the activity of other organs. There are also certain organs of +glandular structure which are called the _ductless glands_; these +are not connected with the surface and all their secretion passes into +the blood. It is a part of recent knowledge that the substances +produced in these glands are of great importance for the body, some of +them even essential for the maintenance of life. In front of the neck +is such an organ, the thyroid gland (Fig. 8, 14). Imperfect +development or absence of this organ, or an inactive condition of it, +produces in the child arrested growth and deficient mental development +known as cretinism, and in the adult the same condition gives rise to +mental deterioration, swelling of the skin, due to a greater content +of water, and loss of hair. This deficiency in the production of +thyroid secretion can be made good and the symptoms removed by feeding +the patient with similar glands removed from animals. The very complex +disease known as exophthalmic goitre, and shown by irregular and rapid +action of the heart, protruding eyeballs and a variety of mental +symptoms, is also associated with this gland, and occasioned not by a +deficiency but by an excess or perversion of its secretion. + +Adjoining the thyroid there are four small glands, the parathyroids, +each about the size of a split pea. The removal of these glands in +animals produces a condition resembling acute poisoning accompanied by +spasmodic contraction of the muscles. A small glandular organ at the +base of the brain, the pituitary body, produces a secretion, one of +the most marked properties of which is a control of growth, +particularly that of the bones. Most cases of giantism, combined as +they are with imperfect mentality, are due to disease of this gland. +There are glands near the kidney which regulate the pressure of the +blood in the arteries by causing contraction of their muscular walls. +The sexual characteristics in the male and female are due to an +internal secretion produced by the respective sexual glands which +affects growth, body development and mentality. + +So is the body constituted. A series of surfaces, all connected, of +enormous size, which enclose a large number of organs and tissues, the +activities of which differ, but all are cooerdinated to serve the +purposes of the organism as a whole. We should think of the body not +as an assemblage of more or less independent entities, but as a single +organism in which all parts are firmly knit together both in structure +and in function, as are the components of a single cell. + +FOOTNOTES: +[1] They do, however, take place, since within comparatively +few years whole species have completely disappeared; for example, the +great auk and the passenger pigeon. In these cases it is not known +what part disease played in the destruction. + +[2] A tissue represents an aggregate of similar cells with +the intercellular substances in relation with these as connective +tissue, muscular tissue, etc. Where such cell aggregates are localized +and where the cells are arranged in structures having definite form +and size and performing a definite function, it is customary to +designate such structures as organs, as the brain, liver, etc. + + + + +CHAPTER II + +NO SHARP LINE OF DEMARKATION BETWEEN HEALTH AND DISEASE.--THE +FUNCTIONAL NUTRITIVE AND FORMATIVE ACTIVITIES OF CELLS.--DESTRUCTION +AND REPAIR CONSTANT PROCESSES IN LIVING MATTER.--INJURIES TO THE +BODY.--THE EFFECT OF HEAT.--THE ACTION OF POISONS.--THE LESIONS OF +DISEASE.--REPAIR.--THE LAWS GOVERNING REPAIR.--RELATION OF REPAIR TO +COMPLEXITY OF STRUCTURE AND AGE.--THE RESERVE FORCE OF THE BODY.-- +COMPENSATORY PROCESSES IN THE BODY.--OLD AGE.--THE DIMINUTION OF +RESISTANCE TO THE EFFECT OF THE ENVIRONMENT A PROMINENT FACTOR IN OLD +AGE.--DEATH.--HOW BROUGHT ABOUT.--CHANGES IN THE BODY AFTER DEATH.-- +THE RECOGNITION OF DEATH. + + +There is no sharp line separating health from disease; changes in the +tissues of the same nature, or closely akin to those which are found +in disease, are constantly occurring in a state of health. The +importance of parasites in causing disease has led to the conception +of disease as almost synonymous with parasitism; but it must be +remembered that the presence of parasites living at the expense of the +body is perfectly consistent with a state of health. Degeneration, +decay and parasitism only become disease factors when the conditions +produced by them interfere with the life which is the normal or usual +for the individual concerned. + +All the changes which take place in the cells are of great importance +in conditions of both health and disease, for life consists in +cooerdinated cell activity. The activities of the cells can be divided +into those which are nutritive, those which are functional and those +which are formative. In the functional activity the cell gives off +energy, this loss being made good by the receipt of new energy in the +form of nutritive material with which the cell renews itself. In +certain cells an exact balance seems to be maintained, but in those +cells whose activity is periodic function takes place at the expense +of the cell substance, the loss being restored by nutrition during the +period of repose. This is shown particularly well in the case of the +nerve cells (Fig. 13). Both the functional and nutritive activity can +be greatly stimulated, but they must balance; otherwise the condition +is that of disease. + +[Illustration: FIG 13.--NERVE CELLS OF AN ENGLISH SPARROW (_a_) Cells +after a day's full activity, (_b_) cells after a night's repose. In +(_a_) the cells and nuclei are shrunken and the smaller clear spaces +in the cells are smaller and less evident than in (_b_). (Hodge)] + +The formative activity of cells is also essential to the normal state. +Destruction of cells is constantly taking place in the body, and more +rapidly in certain tissues than in others. Dried and dead cells are +constantly and in great numbers thrown off from the surface of the +skin: such epidermic appendages as the hair and nails grow and are +removed, millions of cells are represented in the beard which is daily +removed. Cells are constantly being destroyed on the intestinal +surface and in the glands. There is an enormous destruction of the +blood cells constantly taking place, certain essential pigments, as +that of the bile, being formed from the haemoglobin which the red blood +corpuscles contain and which becomes available on their destruction. +All such loss of cells must be made good by the formation of new ones +and, as in the case of the nutritive and functional activity, the loss +and renewal must balance. The formative activity of cells is of great +importance, for it is by means of this that wounds heal and diseases +are recovered from. This constant destruction and renewal of the body +is well known, and it is no doubt this which has given rise to the +belief, widely held, that the body renews itself in seven years and +that the changes impressed upon it by vaccination endure for this +period only. The truth is that the destruction and renewal of most +tissues in the body takes place in a much shorter interval, and, as we +shall see, this has nothing to do with the changes concerned in +vaccination. All these activities of the cells vary in different +individuals, in different parts and at different ages. + +The lesions or injuries of the body which form so prominent a part of +disease vary in kind, degree and situation, depending upon the +character of the injurious agent, the duration of its action and the +character of the tissue affected. The most obvious injuries are those +produced by violence. By a cut, blood vessels are severed, the +relations of tissues disturbed, and at the gaping edges of the wound +the tissue usually protected by the skin is exposed to the air, +resulting in destruction of the cells contained in a thin layer of the +surface. The discoloration and swelling of the skin following a blow +is due to rupture of vessels and escape of blood and fluid, and +further injury may result from the interruption of the circulation. + +By the application of heat the tissue may be charred and the albumen +of the blood and tissue fluids coagulated. Living cells are very +susceptible to the action of heat, a temperature of 130 degrees being +the thermal death point, and even lower temperatures are fatal when +their action is prolonged. The action of the heat may produce definite +coagulation of the fluid within the cells in the same way that the +white of an egg is coagulated. Certain of the albumens of the body +coagulate at a much lower temperature than the white of the egg (as +the myosin, one of the albumens of the muscle which coagulates at 115 deg. +F., egg white coagulating at 158 deg. F.), and in addition to such +coagulation or without it the ferments within the cell and to the +action of which cellular activity is due may be destroyed. + +In diseases due to parasites, the parasite produces a change in the +tissue in its immediate vicinity often so great as to result in the +death of the cells. The most general direct cause of lesions is toxic +or poisonous substances, either introduced from without or formed in +the body. In the case of the parasitic diseases the mere presence of +the parasite in the body produces little or no harm, the injury being +caused by poisons which it produces, and which act both locally in the +vicinity of the parasite and at a distance, being absorbed and +entering the blood stream. How certain of the poisonous substances act +is easy to see. Strong caustics act by coagulating the albumen, or by +the withdrawal of water from the cell. Other poisons act by forming +stable chemical compounds with certain of the cell constituents and +thereby preventing the usual chemical processes from taking place. +Death from the inhalation of illuminating gas is due to the carbon +monoxide contained in this, forming a firm chemical union with the +haemoglobin of the red corpuscles so that the function of these as +oxygen carriers is stopped. + +In order that most poisons may act, it is essential that they enter +into the cell, and they cannot do this unless they are able to combine +chemically with certain of the cell constituents. To this is due the +selective action of many poisons. Morphine, for example, acts chiefly +on the cells of the brain; strychnine acts on the cells of the spinal +cord which excite motion and thus causes the characteristic muscular +spasm. The poisonous substances produced by bacteria, as in the case +of diphtheria, act on certain of the organs only. Different animal +species owe their immunity to certain poisons to their cells being so +constituted that a poison cannot gain entrance into them; pigeons, for +example, cannot be poisoned by morphia. Individual variations play an +important part also; thus, shellfish are poisonous for certain +individuals and not so for others. Owing to the variability of living +structures a substance may be poisonous at one time and not at +another, as the following example shows. A man, very fond of crab +meat, was once violently poisoned after eating crabs, being at that +time seemingly in his usual state of health, and no illness resulted +in others who had partaken of the same crabs. Two months later a +hearty meal of crabs produced no ill result. There are also +individuals so constituted that so simple a food as the egg is for +them an active poison. + +The lesions produced by the action of injurious conditions are usually +so distinctive in situation and character that by the examination of +the body after death the cause of death can be ascertained. The +lesions of diseases may be very obvious to the naked eye, or in other +cases only the most careful microscopic examination can detect even +the presence of alterations. In the case of poisons the capacity of +the cell for adaptation to unusual conditions is of great importance. +It is probable that certain changes take place within the cells, owing +to which the function can be continued in spite of the unusual +conditions which the presence of the poison brings about. It is in +this way that the habitual use of such poisons as morphine, alcohol +and tobacco, to speak only of those best known, is tolerated. The cell +life can become so accustomed to the presence of poisons that the cell +activities may suffer in their absence. + +_Repair_ of the injuries which the body receives is effected in a +variety of ways. We do not know how intracellular repair takes place, +but most probably the cells get rid of the injured areas either by +ejecting them, or chemical changes are produced in the altered cell +substance breaking up and recombining the molecules. When single cells +are destroyed, the loss is made good by new formation of cells, the +cell loss stimulating the formative activity of the cells in the +vicinity. The body maintains a cell and tissue equilibrium, and a loss +is in most cases repaired. The blood fluid lost in a haemorrhage is +quickly restored by a withdrawal of the fluid from the tissues into +the blood, but the cells lost are restored by new formation of cells +in the blood-forming organs. The blood cells are all formed in bone +marrow and in the lymph nodes, and not from the cells which circulate +in the blood, and the stimulus to new cell formation which the loss of +blood brings about affects this remote tissue. + +In general, repair takes place most easily in tissues of a simple +character, and where there is the least differentiation of cell +structure for the purposes of function. A high degree of function in +which the cell produces material of a complex character necessitates a +complex chemical apparatus to carry this out, and a complicated +mechanism is formed less easily than a simple one. In certain tissues +the cells have become so highly differentiated that all formative +activity is lost. Such is the case in the nerve cells of the brain and +spinal cord, a loss in which tissue is never repaired by the formation +of new cells; and in the muscles the same is true. The least +differentiation is seen in those cells which serve the purpose of +mechanical protection only, as the cells of the skin, and in these the +formative activity is very great. Not only must the usual loss be +supplied, but we are all conscious of slight injuries of the surface +which are quickly repaired. + +Repair, other things being equal, takes place more easily in the young +than in the old. New formation of cells goes on with great rapidity in +intra-uterine life, the child, beginning its existence as a single +cell one two hundred and fiftieth of an inch in diameter, attains in +nine months a weight of seven pounds. The only similar rapidity of +cell formation is seen in certain tumors; although the body may add a +greater amount of weight and in a shorter time, by deposit of fat, +this in but slight measure represents a new formation of tissue, but +is merely a storage of food material in cells. The remarkable repair +and even the new formation of entire parts of the body in the tadpole +will not take place in the completely developed frog. + +Repair will also take place the more readily the less complicated is +the architectural structure of the part affected. When a series of +tissues variously and closely related to one another enter into the +structure of an organ, there may be new formation of cells; but when +the loss involves more than this, the complicated architectural +structure will not be completely replaced. A brick which has been +knocked out of a building can be easily replaced, but the renewal of +an area of the wall is more difficult. In the kidney, for example, the +destruction of single cells is quickly made good by new cell +formation, but the loss of an area of tissue is never restored. In the +liver, on the other hand, which is of much simpler construction, large +areas of tissue can be newly formed. For the formation of new cells in +a part there must be a sufficient amount of formative material; then +the circulation of the blood becomes more active, more blood being +brought to the part by dilatation of the vessels supplying it. + +Repair after a loss can be perfect or imperfect. The tissue lost can +be restored so perfectly that no trace of an injury remains; but when +the loss has been extensive, and in a tissue of complex structure, +complete restoration does not take place and a less perfect tissue is +formed which is called a scar. Examination of the skin in almost +anyone will show some such scars which have resulted from wounds. They +are also found in the internal organs of the body as the result of +injuries which have healed. The scar represents a very imperfect +repair. In the skin, for example, the scar tissue never contains such +complicated apparatus as hair and sweat glands; the white area is +composed of an imperfectly vascularized fibrous tissue which is +covered with a modified epidermis. The scar is less resistant than the +normal tissue, injury takes place more easily in it and heals with +more difficulty. + +Loss brought about by the injuries of disease can be compensated for, +even when the healing is imperfect, by increased function of similar +tissue in the body. There always seems to be in the body under the +usual conditions a reserve force, no tissue being worked to its full +capacity. Meltzer has compared the reserve force of the body to the +factor of safety in mechanical construction. A bridge is constructed +to sustain the weight of the usual traffic, but is in addition given +strength to meet unusual and unforeseen demands. The stomach provides +secretion to meet the usual demands of digestion, but can take care of +an unusual amount of food. The work of the heart may be doubled by +severe exertions, and it meets this demand by increased force and +rapidity of contraction; and the same is true of the muscles attached +to the skeleton. The constant exercise of this reserve force breaks +down the adjustment. If the weight of the traffic over the bridge be +constantly all that it can carry, there quickly comes a time when some +slight and unforeseen increase of weight brings disaster. The +conditions in the body are rather better than in the case of the +bridge, because with the increased demand for activity the heart, for +example, becomes larger and stronger, and reserve force rises with the +load to be carried, but the ratio of reserve force is diminished. + +This discussion of injury and repair leads to the question of old age. +Old age, as such, should not be discussed in a book on disease, for it +is not a disease; it is just as natural to grow old and to die as it +is to be born. Disease, however, differs in many respects in the old +as compared with the young and renders some discussion of the +condition necessary. Changes are constantly taking place in the body +with the advance of years, and in the embryo with the advance of days. +In every period of life in the child, in the adult, in the middle-aged +and in the old we meet with conditions which were not present at +earlier periods. There is no definite period at which the changes +which we are accustomed to regard as those of old age begin. This is +true of both the external appearances of age and the internal changes. +One individual may be fully as old, as far as is indicated by the +changes of age, at fifty as another at eighty. + +With advancing age certain organs of the body atrophy; they become +diminished in size, and the microscopic examination shows absence or +diminished numbers of the cells which are peculiar to them. The most +striking example of this is seen in the sexual glands of females, and, +to a less degree, in those of the male. There is a small mass or +glandular tissue at the root of the neck, the thymus, which gradually +grows from birth and reaches its greatest size at the age of fifteen, +when it begins slowly to atrophy and almost disappears at the age of +forty. This is the gland which in the calf is known as the sweetbread +and is a delicious and valued article of food. The tonsils, which in +the child may be so large as to interfere with breathing and +swallowing, have almost disappeared in the adult; and there are other +such examples. + +In age atrophy is a prominent change. It is seen in the loss of the +teeth, in the whitening and loss of the hair, in the thinning of the +skin so that it more easily wrinkles, in the thinning and weakening of +the muscles so that there is not only diminished force of muscular +contraction, but weakening of the muscles of support. The back curves +from the action of gravity, the strength of the support of the muscles +at the back not counteracting the pull of the weight of the abdominal +viscera in front. The bones become more porous and more brittle. + +The effect of atrophy is also seen in the diminution of all functions, +and in loss of weight in individual organs. That the brain shares in +the general atrophy is evident both anatomically and in function. +Mental activity is more sluggish, impressions are received with more +difficulty, their accuracy may be impaired by accompanying changes in +the sense organs, and the concepts formed from the impressions may +differ from the usual. The slowness of mental action and the +diminution in the range of mental activity excited by impressions, and +the slowness of expression, may give a false idea of the value of the +judgment expressed. The expression changes, the face becomes more +impassive because the facial muscles no longer reflect the constant +and ever changing impressions which the youthful sense organs convey +to a youthful and active brain. That the young should ape the old, +should seek to acquire the gravity of demeanor, to restrain the quick +impulse, is not of advantage. Loss of weight of the body as a whole is +not so apparent, there being a tendency to fat formation owing to the +non-use of fat or fat-forming material which is taken into the body. +One of the most evident alterations is a general diminution in the +fluid of the tissues, to which is chiefly due the lack of plumpness, +the wrinkles of age. The facial appearance of age is given to an +infant when, in consequence of a long-continued diarrhoea, the tissues +become drained of fluid. Every market-man knows that an old animal is +not so available for food, the tissues are tougher, more fibrous, not +so easily disintegrated by chewing. This is due to a relative increase +in the connective tissue which binds all parts together and is +represented in the white fibres of meat. + +Senile atrophy is complex in its causes and modes of production. The +atrophy affects different organs in different degree and shows great +variation in situation, in degree and in progress. Atrophic changes of +the blood vessels are of great importance, for this affects the +circulation on which the nutrition of all tissues depends. While there +is undoubted progressive wear of all tissues, this becomes most +evident in the case of the blood vessels of the body. It is rare that +arteries which can be regarded as in all respects normal are found in +individuals over forty, and these changes progress rapidly with +advancing age. So striking and constant are these vascular changes +that they seem almost in themselves sufficient to explain the senile +changes, and this has been frequently expressed in the remark that age +is determined not by years, but by the condition of the arteries. +Comparative studies show the falsity of this view, for animals which +are but little or not at all subject to arterial disease show senile +changes of much the same character as those found in man. + +There is another condition which must be considered in a study of +causes of age. In the ordinary course of life slight injuries are +constantly being received and more or less perfectly repaired. An +infection which may but slightly affect the ordinary well-being of the +individual may produce a considerable damage. Excess or deficiency or +improper food, occasional or continued use of alcohol and other +poisons may lead to very definite lesions. Repair after injury is +rarely perfect, the repaired tissue is more susceptible to injury, and +with advancing age there is constant diminution in the ease and +perfection of repair. The effect of the sum of all these changes +becomes operative: a vicious circle is established in which injury +becomes progressively easier to acquire and repair constantly less +perfect. There is some adjustment, however, in that the range of +activities is diminished, the environment becomes narrower and the +organism adapts its life to that environment which makes the least +demands upon it. + +Whether there is, entirely apart from all conditions affecting +nutrition and the effect of injuries which disturb the usual cell +activities, an actual senescence of the cells of the body is +uncertain. In the presence of the many factors which influence the +obvious diminution of cell activity in the old, it is impossible to +say whether the loss of cell activity is intrinsic or extrinsic. The +life of the plant cell seems to be immortal; it does not grow old. +Trees die owing to accidents or because the tree acquires in the +course of its growth a mass of tissue in which there is little or no +life, and which becomes the prey of parasites. The growing tissue of a +tree is comprised in a thin layer below the bark, and the life of this +may seemingly be indefinitely prolonged by placing it in a situation +in which it escapes the action of accidental injuries and decay, as by +grafting on young trees. Where the nature of the dead wood is such +that it is immune from parasites and decay, as in the case of the +Sequoias, life seems to be indefinitely prolonged. The growing +branches of one of these trees, whose age has been estimated with +seeming accuracy at six thousand years, are just as fresh and the tree +produces its flowers and fruit in the same degree as a youthful +brother of one thousand years. Nor does old age supervene in the +unicellular organisms. An amoeba assimilates, grows and multiplies +just as long as the environment is favorable. + +Old age in itself is seldom a cause of death. In rare cases in the +very old a condition is found in which no change is present to which +death can be attributed, all organs seem to share alike in the +senescence. Death is usually due to some of the accidents of life, a +slight infection to which the less resistant body succumbs, or to the +rupture of a weakened blood vessel in the brain, or to more advanced +decay in some organ whose function is indispensable. The causes and +conditions of age have been a fertile source for speculation. Many of +the hypotheses have been interesting, that of Metschnikoff, for +example, who finds as a dominating influence in causing senescence the +absorption of toxic substances formed in the large intestine by +certain bacteria. He further finds that the cells of the body which +have phagocytic powers turn their activity against cells and tissues +which have become weakened. There may be absorption of injurious +substances from the intestines which the body in a vigorous condition +is able to destroy or to counteract their influence, and these may be +more operative in the weaker condition of the body in the old. +Phagocytes will remove cells which are dead and often cells which are +superfluous in a part, but there is no evidence that this is ever +other than a conservative process. Since it is impossible to single +out any one condition to which old age is due, the hypothesis of +Metschnikoff should have no more regard given it than the many other +hypotheses which have been presented. + +Death of the body as a whole takes place from the cessation of the +action of the central nervous system or of the respiratory system or +of the circulation. There are other organs of the body, such as the +intestine, kidney, liver, whose function is essential for life, but +death does not take place immediately on the cessation of their +function. The functions of the heart, the brain and the lungs are +intimately associated. Oxygen is indispensable for the life of the +tissues, and its supply is dependent upon the integrity of the three +organs mentioned, which have been called the tripos of life. +Respiration is brought about by the stimulation of certain nerve cells +in the brain, the most effective stimulus to these cells being a +diminution of oxygen in the blood supplying them. These cells send out +impulses to the muscles concerned in inspiration, the chest expands, +and air is taken into the lungs. Respiration is then a more +complicated process than is the action of the heart, for its +contraction, which causes the blood to circulate, is not immediately +dependent upon extrinsic influences. Death is usually more immediately +due to failure of respiration than to failure of circulation, for the +heart often continues beating for a time after respiration has ceased. +Thus, in cases of drowning and suffocation, by means of artificial +respiration in which air is passively taken into and expelled from the +lungs, giving oxygen to the blood, the heart may continue to beat and +the circulation continue for hours after all evident signs of life and +all sensation has ceased. + +By this general death is meant the death of the organism as a whole, +but all parts of the body do not die at the same time. The muscles and +nerves may react, the heart may be kept beating, and organs of the +body when removed and supplied with blood will continue to function. +Certain tissues die early, and the first to succumb to the lack of +oxygenated blood are the nerve cells of the brain. If respiration and +circulation have ceased for as short a time as twelve minutes, life +ceases in certain of these cells and cannot be restored. This is again +an example of the greater vulnerability of the more highly +differentiated structure in which all other forms of cell activity are +subordinated to function. There are, however, pretty well +authenticated cases of resuscitation after immersion in water for a +longer period than twelve minutes, but these cases have not been +carefully timed, and time under such conditions may seem longer than +it actually is; and there is, moreover, the possibility of a slight +gaseous interchange between the blood and the water in the lungs, as +in the case of the fish which uses the water for an oxygen supply as +the mammal does the air. There are also examples of apparent death or +trances which have lasted longer, and the cases of fakirs who have +been buried for prolonged periods and again restored to life. In these +conditions, however, all the activities of the body are reduced to the +utmost, and respiration and circulation, so feeble as to be +imperceptible to ordinary observation, suffice to keep the cells +living. + +With the cessation of life the body is subject to the unmodified +action of its physical environment. There is no further production of +heat and the body takes the temperature of the surroundings. The only +exceptions are rare cases in which such active chemical changes take +place in the dead body that heat is generated by chemical action. At a +varying interval after death, usually within twelve hours, there is a +general contraction and hardening of the muscles due to chemical +changes, probably of the nature of coagulation, in them. This begins +in the muscles of the head, extends to the extremities, and usually +disappears in twenty-four hours. It is always most intense and most +rapid in its onset when death is preceded by active muscular exertion. +There have been cases of instantaneous death in battle where the body +has remained in the position it held at the moment of death, this +being due to the instantaneous onset of muscular rigidity. The blood +remains fluid for a time after death and settles in the more dependent +parts of the body, producing bluish red mottled discolorations. Later +the blood coagulates in the vessels. The body loses moisture by +evaporation. Drying of the surface takes place where the epidermis is +thin, as over the transparent part of the eye and over areas deprived +of epidermis. Decomposition and putrefaction of the body due to +bacterial action takes place. The bacteria ever present in the +alimentary canal make their way from this into the dead tissue. +Certain of these bacteria produce gas which accumulates in the tissues +and the body often swells enormously. A greenish discoloration +appears, which is due to the union of the products of decomposition +with the iron in the blood; this is more prominent over the abdomen +and appears in lines along the course of the veins. The rapidity with +which decomposition takes place varies, and is dependent upon many +factors, such as the surrounding temperature, the nutrition of the +body at the time of death, the cause of death. It is usually not +difficult to recognize that a body is dead. In certain cases, however, +the heart's action may be so feeble that no pulse is felt at the +wrist, and the current of the expired air may not move a feather held +to the nostril or cloud the surface of a mirror by the precipitation +of moisture upon it. This condition, combined with unconsciousness and +paralysis of all the voluntary muscles, may very closely simulate +death. The only absolute evidence of death is given by such changes as +loss of body heat, rigor mortis or stiffening of the muscles, +coagulation of the blood and decomposition. + + + + +CHAPTER III + +THE GROWTH OF THE BODY.--GROWTH MORE RAPID IN EMBRYONIC PERIOD.--THE +COOeRDINATION AND REGULATION OF GROWTH.--TUMORS.--THE GROWTH OF TUMORS +COMPARED WITH NORMAL GROWTH.--SIZE, SHAPE AND STRUCTURE OF TUMORS.-- +THE GROWTH CAPACITY OF TUMORS AS SHOWN BY THE INOCULATION OF TUMORS OF +MICE.--BENIGN AND MALIGNANT TUMORS.--EFFECT OF INHERITANCE.--ARE +TUMORS BECOMING MORE FREQUENT?--THE EFFECT PRODUCED BY A TUMOR ON THE +INDIVIDUAL WHO BEARS IT.--RELATION OF TUMORS TO AGE AND SEX.--THEORIES +AS TO THE CAUSE OF TUMORS.--THE PARASITIC THEORY.--THE TRAUMATIC +THEORY.--THE EMBRYONIC THEORY.--THE IMPORTANCE OF THE EARLY +RECOGNITION AND REMOVAL OF TUMORS. + + +The power of growth is possessed by every living thing, but growth is +not limited to the living. Crystals also will grow, and the rapidity +and character of growth and the maximum size of the crystal depends +upon the character of the substance which forms the crystal. From the +single cell or ovum formed by the union of the male and female sexual +cells, growth is continuous until a size corresponding to the type of +the species is attained. From this time onward growth is limited to +the degree necessary to supply the constant loss of material which the +body undergoes. The rapidity of the growth of the body and of its +component parts differs at different ages, and becomes progressively +less active from its beginning in the ovum until the adult type of the +species is attained. As determined by the volume, the embryo increases +more than ten thousand times in size during the first month of +intra-uterine life. At birth the average weight is six and a half +pounds; at the end of the first year eighteen and a half pounds, a +gain of twelve pounds; at the end of the second year twenty-three +pounds, a gain of four and a half pounds. The growth is cooerdinated, +the size of the single organs bearing a definite ratio, which varies +within slight limits, to the size of the body, a large individual +having organs of corresponding size. Knowing that the capacity of +growth is one of the inherent properties of living matter, it is much +easier to understand the continuance of growth than its cessation. It +is impossible to avoid the conclusion that there is some internal +mechanism of the body which controls and regulates growth. In the +first chapter reference was made to organs producing substances which +pass directly into the circulation; these substances act by control of +the activities of other parts, stimulating or depressing or altering +their function. Two of these glands, the thymus, lying in front, where +the neck joins the body and which attains its greatest size at +puberty, and the pituitary body, placed beneath the brain but forming +no part of it, have been shown by recent investigations to have a very +definite relation to growth, especially the growth of the skeleton. +The growth energy chiefly resides in the skeleton, and if the growing +animal has a diet sufficient only to maintain the body weight, the +skeleton will continue to grow at the expense of the other tissues, +literally living upon the rest of the body. Disease of the glands +mentioned leading to an increase or diminution or alteration of their +function may not only inhibit or unduly increase the growth of the +skeleton, but may also interfere with the sexual development which +accompanies the skeleton growth. + +The difficulties which arise in an endeavor to comprehend normal +growth are greater when the growth of tumors is considered. A tumor is +a mass of newly formed tissue which in structure, in growth, and the +relations which it forms with adjoining tissues departs to a greater +or less degree from the type of the tissue to which it is related in +structure or from which it originates. It is an independent structure +which, like a parasite, grows at the expense of the body, contributing +nothing to it, and its capacity for growth is unlimited. A tumor +cannot be considered as an organ, its activities not being coordinated +with those of the body. A part of the body it certainly is, but in the +household economy it is to be considered as a wild and lawless guest, +not influenced by or conforming with the regulations of the household. +The rapidity of growth varies; certain tumors for years increase but +little in size, while others may be seen to increase from day to day. +The growth is often intermittent, periods of great activity of growth +alternating with periods of quiescence. The nutrition and growth of a +tumor is only slightly influenced by the condition of nutrition of the +bearer. Its cells have a greater avidity for food than have those of +the body, and, like the growing bones of an insufficiently fed animal, +growth in some cases seems to take place at the expense of the body, +the normal cells not obtaining sufficient nutriment to repair their +waste. + +A tumor may be of any size: so small as to be invisible to the naked +eye, or its weight may exceed that of the individual who bears it. The +limitations to its growth are extrinsic and not intrinsic. There is no +distinct color. Certain tumors have color which depends upon the +presence of a dark brown or black pigment within the cells. +Haemorrhages within them are not infrequent, and they may be colored by +the blood or by pigments formed from it. Usually they have a gray +color modified by their varying vascularity, or the cut surface may be +mottled due to areas of cell degeneration. The consistency varies; +some tumors are so soft that they can be pressed through a sieve, +others are of stony hardness. There is no distinct shape, this being +influenced by the nature of the tumor, the manner of growth and +situation. When the tumor grows on or near a surface, it may project +from this and be attached by a narrow band only; in the interior of +the body it may be irregular in outline, round or lobular, the shape +being influenced by many factors. Tumors like the tissues of the +normal body are nourished by the blood and contain blood vessels often +in great numbers. + +A tumor arises by the cells of a part of the body beginning to grow +and taking on the characteristics of a tumor. Its growth is +independent, the cells of the adjoining tissue taking no part in it. +The tissue in the vicinity of the tumor is partly pushed aside by the +mass, or the tumor grows into it and the tissue disappears as the +tumor advances. The destruction of the surrounding tissue is brought +about partly by the pressure which the tumor exerts, partly by the +compression of the blood vessels or the blood supply of the organs is +diverted to the tumor. + +The characteristics of a tumor are due to the cells which it contains +(Fig 14). These often become separated from the main mass and are +carried by the blood into other parts of the body, where they grow and +form tumors similar in character to the parent tumor. In the +extraordinary capacity for growth possessed by tumor cells, they +resemble vegetable rather than animal cells. There is no limit to the +growth of a tumor save by the death of the individual who bears it, +thus cutting off the supply of nutrition. The cells of tumors peculiar +to man show a narrow range of adaptation. They will grow only in the +body of the individual to whom the tumor belongs, and die when grafted +on another individual. In the case of tumors which arise in animals, +pieces of the tumor when grafted on another animal of the same species +will grow, and in this way the growth capacity of the tumor cells has +been estimated. Thus, by transplanting a small section of a mouse +tumor into other mice, the small transplanted fragments will in two +weeks grow to the size of filberts, and each of these will furnish +material to engraft upon ten mice. These new tumors are similar in +character to the original tumor, and really represent parts of it in +the same way that all the Baldwin apples in the world are parts of the +original tree which was found in Baldwinville many years ago, and as +all the Concord grape vines are really parts of the original vine. It +has been estimated that if all the growth capacity of this mouse tumor +were availed of by the successive inoculation of other mice, a mass of +tumor several times the diameter of the sun would grow in two years. +The condition of the individual seems to exert no influence upon the +growth of the tumor. Growth may be as rapid when the bearer is in a +condition of extreme emaciation as it is when the bearer is well +nourished and robust. + +[Illustration: FIG 14.--PHOTOGRAPH OF A MICROSCOPIC PREPARATION FROM A +CANCER OF THE UTERUS. A large mass of cells is extending into the +tissue of the uterus which is shown as the fibrous structure. Such a +cell mass penetrating into the tissue represents the real cancer, the +tissue about the cell masses bear the blood vessels which nourish the +tumor cells.] + +Those tumors which grow rapidly and invade and destroy the surrounding +tissue are called malignant tumors or cancers, but in a strict sense +no tumor can be regarded as benign, for none can serve a useful +purpose. A tumor after a period of slow growth can begin to grow +rapidly. Tumors may arise in any part of the body, but there are +certain places of preference particularly for the more malignant +tumors. These are places where the cells naturally have a marked power +of growth, and especially where growth is intermittent as in the +uterus and mammary gland. + +Little is known in regard to the influence of inheritance on the +formation of tumors. Study of the tumors of mice show a slightly +greater susceptibility to tumor formation in the progeny of mice who +have developed tumors. Studies of human families seem to show that +heredity has a slight influence, but in the frequency of tumors such +statistical evidence is of little value. The question of inheritance +has much bearing on the origin of tumors. If the tumor is accidental +and due entirely to extraneous causes, inheritance is not probable; +but if there is some predisposition to tumor formation in certain +individuals due to some peculiarity, then inheritance may exert an +influence. + +The question as to whether tumors are an increasing cause of disease +is equally difficult of solution. The mortality statistics, if taken +at their face value, show an enormous increase in frequency; but there +are many factors which must be considered and which render the +decision difficult and doubtful. Tumors are largely a prerogative of +age, and the increased duration of life which preventive medicine has +brought about brings more people into the age when tumors are more +common. Owing to the greater skill in the diagnosis of tumors, +especially those of the internal organs, they are now recognized more +frequently and more deaths are correctly ascribed to them. Deaths from +tumors were formerly often purposely concealed and attributed to some +other cause. + +No age is immune to tumors. They may be present at birth or develop +shortly afterwards. The age from five to twenty years is the most free +from them, that from forty-five to sixty-five the most susceptible, +particularly to the more malignant forms. + +A tumor is a local disease. The growing tissue of the tumor is the +disease, and it is evident that if the entire tumor were removed the +disease would be cured. This is the end sought by surgical +interference, but notwithstanding seemingly thorough removal, the +tumor often reappears after an interval of months or years. There are +many conditions which may render the complete removal of a tumor +difficult or impossible. It is often impossible to ascertain just how +far the tumor cells have invaded the neighboring structures; the +situation of the tumor may be such that an extended removal would +injure organs which are essential for life, or at the time of removal +the tumor cells may have been conveyed elsewhere by the blood or +lymphatic vessels. + +Successful removal depends mainly upon the length of time the tumor +has been growing. At an early stage even the most malignant tumor may +be successfully removed. It is evident from this how disastrous may be +the neglect of proper surgical treatment of a tumor. The time may be +very short between the first evidence of the presence of a tumor and +the development of a condition which would render complete removal +impossible. + +The effect of a tumor upon its bearer depends upon its character and +situation. Pain is very commonly present, and is due to the pressure +which the growing tumor exerts upon the sensory nerves. Pain may, +however, not be present or appear only at the last. A condition of +malnutrition and emaciation often results due to the passage into the +blood of injurious substances formed in the tumor, or to the +destruction of important organs by the growing tumor. The growth of a +tumor in the intestine may obstruct or close the canal and thus +interfere with nutrition. + +The cause or causes of tumors are unknown. We know that the tumor +represents essentially an abnormal growth, and that this growth is due +to new formation of cells. In certain cases the tumor repeats the +structure of the organ or tissue in which it originates, in others it +departs widely from this; always, however, its structure resembles +structures found in the body at some period of life. The tumor cells, +like all other cells of the body, grow by means of the nutriment which +the body supplies; they have no intrinsic sources of energy. The great +problem is what starts the cells to grow and why the growth differs +from that of normal tissue, why it is not regulated and cooerdinated as +are other forms of growth. When a small piece of the skin, for +instance, is cut out growth as rapid as that in tumors takes place in +the adjoining cells, _but it ceases when the loss is restored_. +The same is true when a piece of the liver is removed. + +Various hypotheses have been formed to explain the tumor, all of them +of interest, and they have had great importance in that the attempt to +prove or disprove the hypothesis by continued observation and +experiment along definite lines has produced new knowledge. The +various theories as to cause may be divided into three heads. + +The parasitic theory. This supposes that a living parasite invades the +body, and by its presence excites the cells of certain tissues to grow +in tumor form. It is known that active growth of the cells of the body +can be excited in a number of ways, by chemical substances such as +certain of the coal tar products, and that it often takes place under +the influence of bacteria. It is further known that parasites can +produce tumor-like growths in plants. The large, rough excrescences on +the oaks are produced by a fly which lays its eggs in or beneath the +bark, and the larva which develops from the egg secretes a substance +which causes the cells about it to multiply, and a huge mass is formed +which serves the developing insect for both food and protection. Large +tumor-like masses are formed on the roots and stalk of cabbages as the +result of the invasion of the cells by a minute organism: the tumors +of olive trees are due to a bacterium; the peculiar growths on cedar +trees, the so-called "witches' brooms," are produced by a fungus, and +there are many other such examples. These have many analogies with +tumors in animals. Under the stimulus of the parasite the cells seem +to have unlimited growth capacity and a greater nutritive avidity than +have the normal plant cells; the character of the mass produced +differs as does the tumor, to a greater or less extent, from the +normal growth; on the cedar, for instance, the "witches' broom" +consists of a thick mass of foliage with small stems less green than +the usual foliage, the leaves wider and not so closely applied to the +stems. The entire plant suffers in its nutrition and a condition +resembling tumor cachexia[1] is produced, and there are no fundamental +differences between the plant and animal tumors. Support has also been +given to the parasitic theory by the discovery within tumor cells of +bodies which were supposed to be a peculiar sort of parasite. If the +truth of the parasitic theory could be proved, there would be +justifiable expectation that the tumor disease might be controlled as +are many of the parasitic diseases, but the hypothesis awaits the +demonstration of its correctness. Despite the study of tumors which is +being actively pursued in many places and by the most skilled +investigators, no parasites have been found in animal tumors; the +objects previously described as parasites have been found not to be +such. It is difficult to bring in accord with the parasitic theory the +great variation in tumor structure, the relation of certain tumors, as +the malignant tumors of the breast and uterus, with the age of the +bearer, the congenital tumors which develop in intra-uterine life, and +there are many other conditions which oppose the theory. + +The traumatic[2] theory. There is much in favor of this. In a certain +number of cases tumors do develop at the site of injuries. The +coincidence of injury and tumor is apt to be overestimated because of +the strong tendency to connect succeeding events. Tumors are not most +common on those parts of the body which are most exposed to injury. +They are rare, for instance, on the hands and feet, and very rarely do +they appear at the site of wounds caused by surgical operations. For +those tumors which develop in intra-uterine life it is difficult to +assign injury as a cause. There does, however, seem to be a relation +between tumors and injuries of a certain character. The natives of +Cashmere use in winter for purposes of heat a small charcoal stove +which they bind on the front of the body; burns often result and +tumors not infrequently develop at the site of such burns. Injuries of +tissue which are produced by the X-ray not infrequently result in +tumor formation and years may elapse between the receipt of the injury +and the development of the tumor. These X-ray injuries are of a +peculiar character, their nature but imperfectly understood, and the +injured tissues seem to have lost the capacity for perfect repair. + +In regard to the possible action of both injuries and parasites in +causing tumors, the possibility that their effects on different +individuals may not be the same must be considered. In addition to the +trauma or the parasite which may be considered as extrinsic factors, +there may be conditions of the body, intrinsic factors, which favor +their action in tumor development. The peculiar tissue growth within +the uterus called decidua, which occurs normally in pregnancy and +serves to fasten the developing ovum to the inner lining of the +uterus, may be produced experimentally. This growth depends upon two +factors, an internal secretion derived from the ovary and the +introduction into the uterus of a foreign body of some sort; in the +case of pregnancy the developing embryo acts as the foreign body. It +is not impossible that some variation in the complex relations which +determine normal growth may be one factor, possibly the most +important, in tumor formation. + +Another theory is that the tumor is the result of imperfect embryonic +development. The development of the child from the ovum is the result +of a continued formation and differentiation of cells. A cell mass is +first produced, and the cells in this differentiate into three layers +called ectoderm, entoderm and mesoderm, from which the external and +internal surfaces and the enclosed tissues respectively develop, and +the different organs are produced by growth of the cells of certain +areas of these layers. The embryonic theory assumes that in the course +of embryonic development not all the cell material destined for the +formation of individual organs is used up for this purpose, that +certain of the embryonic cells become enclosed in the developing +organs, they retain the embryonic capacity for growth and tumors arise +from them. There is no doubt that something like this does take place. +There is a relation between malformations due to imperfect development +of the embryo and tumors, the two conditions occurring together too +frequently to be regarded as mere coincidence. Also tumors may occur +in parts of the body in which there is no tissue capable of forming +structures which may be present in the tumors. The theory, however, is +not adequate, but it may be among the factors. + +The problems concerned in the nature and cause of tumors are the most +important in medicine at the present time. No other form of disease +causes a similar amount of suffering and anxiety, which often extends +over years and makes a terrible drain on the sympathy and resources of +the family. The only efficient treatment for tumors at the present +time is removal by surgical operation, and the success of the +operation is in direct ratio to the age of the tumor, the time which +elapses from its beginning development. It is of the utmost importance +that this should be generally recognized, and the facts relating to +tumors become general knowledge. Tumors form one of the most common +causes of death (after the age of thirty-five one in every ten +individuals dies of tumor); medical and surgical resources are, in +many cases, powerless to afford relief and the tumor stands as a bar +to the attainment of the utopia represented by a happy and comfortable +old age, and a quiet passing. Every possible resource should be placed +at the disposal of the scientific investigation of the subject, for +with knowledge will come power to relieve. + +FOOTNOTES: +[1] By cachexia is understood a condition of malnutrition and +emaciation which is usually accompanied by a pale sallow color of the +skin. + +[2] By trauma is understood a wound or injury of any sort. + + + + +CHAPTER IV + +THE REACTIONS OF THE TISSUES OF THE BODY TO INJURIES.--INFLAMMATION.-- +THE CHANGES IN THE BLOOD IN THIS.--THE EMIGRATION OF THE CORPUSCLES OF +THE BLOOD.--THE EVIDENT CHANGES IN THE INJURED PART AND THE MANNER IN +WHICH THESE ARE PRODUCED.--HEAT, REDNESS, SWELLING AND PAIN.--THE +PRODUCTION OF BLISTERS BY SUNBURN.--THE CHANGES IN THE CELLS OF AN +INJURED PART.--THE CELLS WHICH MIGRATE FROM THE BLOOD-VESSELS ACT AS +PHAGOCYTES.--THE MACROPHAGES.--THE MICROPHAGES.--CHEMOTROPISM.--THE +HEALING OF INFLAMMATION.--THE REMOVAL OF THE CAUSE.--CELL REPAIR AND +NEW FORMATION.--NEW FORMATION OF BLOOD-VESSELS.--ACUTE AND CHRONIC +INFLAMMATION.--THE APPARENTLY PURPOSEFUL CHARACTER OF THE CHANGES IN +INFLAMMATION. + + +Injury and repair have already been briefly considered in their +relation to the normal body and to old age; there are, however, +certain phenomena included under the term inflammation which follow +the more extensive injuries and demand a closer consideration than was +given in Chapter II. These phenomena differ in degree and character; +they are affected by the nature of the injurious agent and the +intensity of its action, by the character of the tissue which is +affected and by variations in individual resistance to injury. A blow +which would have no effect upon the general surface of the body may +produce serious results if it fall upon the eye, and less serious +results for a robust than for a weak individual. + +Most of the changes which take place after an injury and their +sequence can be followed under the microscope. If the thin membrane +between the toes of a living frog be placed under the microscope the +blood vessels and the circulating blood can be distinctly seen in the +thin tissue between the transparent surfaces. The arteries, the +capillaries and veins can be distinguished, the arteries by the +changing rapidity of the blood stream within them, there being a +quickening of the flow corresponding with each contraction of the +heart; the veins appear as large vessels in which the blood flows +regularly (Fig. 11). Between the veins and arteries is a large number +of capillaries with thin transparent walls and a diameter no greater +than that of the single blood corpuscles; they receive the blood from +the arteries and the flow in them is continuous. The white and red +blood corpuscles can be distinguished, the red appearing as oval discs +and the white as colorless spheres. In the arteries and veins the red +corpuscles remain in the centre of the vessels appearing as a rapidly +moving red core, and between this core and the wall of the vessels is +a layer of clear fluid in which the white corpuscles move more slowly, +often turning over and over as a ball rolls along the table. + +If, now, the web be injured by pricking it or placing some irritating +substance upon it, a change takes place in the circulation. The +arteries and the veins become dilated and the flow of blood more +rapid, so rapid, indeed, that it is difficult to distinguish the +single corpuscles. In a short while the rapidity of flow in the +dilated vessels diminishes, becoming slower than the normal, and the +separation between the red and white corpuscles is not so evident. In +the slowly moving stream the white corpuscles move much more slowly +than do the red, and hence accumulate in the vessels lining the inner +surface and later become attached to this and cease to move forward. +The attached corpuscles then begin to move as does an amoeba, sending +out projections, some one of which penetrates the wall, and following +this the corpuscles creep through. Red corpuscles also pass out of the +vessels, this taking place in the capillaries; the white corpuscles, +on the other hand, pass through the small veins. Not only do the white +corpuscles pass through the vessels, but the blood fluid also passes +out. The corpuscles which have passed into the tissue around the +vessels are carried away by the outstreaming fluid, and the web +becomes swollen from the increased amount of fluid which it contains. +The injured area of the web is more sensitive than a corresponding +uninjured area and the foot is more quickly moved if it be touched. If +the injury has been very slight, observation of the area on the +following day will show no change beyond a slight dilatation of the +vessels and a great accumulation of cells in the tissue. + +Everyone has experienced the effect of such changes as have been +described in this simple experiment. An inflamed part on the surface +of the body is redder than the normal, swollen, hot and painful. The +usual red tinge of the skin is due to the red blood contained in the +vessels, and the color is intensified when, owing to the dilatation, +the vessels contain more blood. The inflamed area feels hot, and if +the temperature be taken it may be two or three degrees warmer than a +corresponding area. The increased heat is due to the richer +circulation. Heat is produced in the interior of the body chiefly in +the muscles and great glands, and the increased afflux of blood brings +more heat to the surface. A certain degree of swelling of the tissue +is due to the dilatation of the vessels; but this is a negligible +factor as compared with the effect of the presence of the fluid and +cells of the exudate.[1] The fluid distends the tissue spaces, and it +may pass from the tissue and accumulate on surfaces or in the large +cavities within the body. The greatly increased discharge from the +nose in a "cold in the head" is due to the exudation formed in the +acutely inflamed tissue, and which readily passes through the thin +epithelial covering. Various degrees of inflammation of the skin may +be produced by the action of the sun, the injury being due not to the +heat but to the actinic rays. In a mild degree of exposure only +redness and a strong sense of heat are produced, but in prolonged +exposure an exudate is formed which causes the skin to swell and +blisters to form, these being due to the exudate which passes through +the lower layers of the cells of the epidermis and collects beneath +the impervious upper layer, detaching this from its connections. If a +small wad of cotton, soaked in strong ammonia, be placed on the skin +and covered with a thimble and removed after two minutes, minute +blisters of exudate slowly form at the spot. + +The pain in an inflamed part is due to a number of factors, but +chiefly to the increased pressure upon the sensory nerves caused by +the exudate. The pain varies so greatly in degree and character that +parts which ordinarily have little sensation may become exquisitely +painful when inflamed. The pain is usually greater when the affected +part is dense and unyielding, as the membranes around bones and teeth. +The pain is often intermittent, there being acute paroxysms +synchronous with the pulse, this being due to momentary increase of +pressure when more blood is forced into the part at each contraction +of the heart. The pain may also be due to the direct action of an +injurious substance upon the sensory nerves, as in the case of the +sting of an insect where the pain is immediate and most intense before +the exudate has begun to appear. + +When an inflamed area is examined, after twenty-four hours, by +hardening the tissue in some of the fluids used for this purpose and +cutting it into very thin slices by means of an instrument called a +microtome, the microscope shows a series of changes which were not +apparent on naked eye examination. The texture is looser, due to the +exudate which has dilated all the spaces in the tissue. Red and white +corpuscles in varying numbers and proportions infiltrate the tissue; +all the cells which belong to the part, even those forming the walls +of the vessels, are swollen, the nuclei contain more chromatin, and +the changes in the nuclei which indicate that the cells are +multiplying appear. The blood vessels are dilated, and the part in +every way gives the indication of a more active life within it. There +are also evidences of the tissue injury which has called forth all the +changes which we have considered. (Fig. 15.) + +[Illustration: FIG. 15--A SECTION OF AN INFLAMED LUNG SHOWING THE +EXUDATE WITHIN THE AIR SPACES. Compare this with Fig 6. Fig 15 is from +the human lung, in which the air spaces are much larger than in the +mouse.] + +The microscopic examination of any normal tissue of the body shows +within it a variable number of cells which have no intimate +association with the structure of the part and do not seem to +participate in its function. They are found in situations which +indicate that these cells have power of active independent motion. In +the inflamed tissue a greatly increased number of these cells is +found, but they do not appear until the height of the process has +passed, usually not before thirty-six or forty-eight hours after the +injury has been received. The numbers present depend much upon the +character of the agent which has produced the injury, and they may be +more numerous than the ordinary leucocytes which migrate from the +blood vessels. + +All these changes which an injured part undergoes are found when +closely analyzed to be purposeful; that is, they are in accord with +the conditions under which the living matter acts, and they seem to +facilitate the operation of these conditions. It has been said that +the life of the organism depends upon the cooerdinated activity of the +living units or cells of which it is composed. The cells receive from +the blood material for the purpose of function, for cell repair and +renewal, and the products of waste must be removed. In the injury +which has been produced in the tissue all the cells have suffered, +some possibly displaced from their connections, others may have been +completely destroyed, others have sustained varying degrees of injury. +If the injury be of an infectious character, that is, produced by +bacteria, these may be present in the part and continue to exert +injury by the poisonous substances which they produce, or if the +injury has been produced by the action of some other sort of poison, +this may be present in concentrated form, or the injury may have been +the result of the presence of a foreign body in the part. Under these +conditions, since the usual activities of the cells in the injured +part will not suffice to restore the integrity of the tissue, repair +and cell formation must be more active than usual, any injurious +substances must be removed or such changes must take place in the +tissue that the cell life adapts itself to new conditions. + +[Illustration: FIG. 16.--PHAGOCYTOSIS. _a_, _b_, _c_ are the +microphages or the bacterial phagocytes. (_a_) Contains a number of +round bacteria, and (_b_) similar bacteria arranged in chains, and +(_c_) a number of rod-shaped bacteria (_d_) Is a cell phagocyte or +macrophage which contains five red blood corpuscles.] + +All life in the tissues depends upon the circulation of the blood. +There is definite relation between the activity of cells and the blood +supply; a part, for instance, which is in active function receives a +greater supply of blood by means of dilatation of the arteries which +supply it. If the body be exactly balanced longitudinally on a +platform, reading or any exercise of the brain causes the head end to +sink owing to the relatively greater amount of blood which the brain +receives when in active function. The regulation of the blood supply +is effected by means of nerves which act upon the muscular walls of +the arteries causing, by the contraction or the relaxation of the +muscle, diminution or dilatation of the calibre of the vessel. After +injury the dilatation of the vessels with the greater afflux of blood +to the part is the effect of the greatly increased cell activity, and +is a necessity for this. In many forms of disease it has been found +that by increasing the blood flow to a part and producing an active +circulation in it, that recovery more readily takes place and many of +the procedures which have been found useful in inflammation, such as +hot applications, act by increasing the blood flow. So intimate is the +association between cell activity, as shown in repair and new +formation of cells, and the blood flow, that new blood vessels +frequently develop by means of which the capacity for nutrition is +still more increased. The cornea or transparent part of the eye +contains no blood vessels, the cells which it contains being nourished +by the tissue fluid which comes from the outside and circulates in +small communicating spaces. If the centre of the cornea be injured, +the cells of the blood vessels in the tissue around the cornea +multiply and form new vessels which grow into the cornea and appear as +a pink fringe around the periphery; when repair has taken place the +newly formed vessels disappear. + +The exudate from the blood vessels in various ways assists in repair. +An injurious substance in the tissue may be so diluted by the fluid +that its action is minimized. A small crystal of salt is irritating to +the eye, but a much greater amount of the same substance in dilute +solution causes no irritation. The poisonous substances produced by +bacteria are diluted and washed away from the part by the exudate. Not +only is there a greater amount of tissue fluid in the inflamed part, +but the circulation of this is also increased, as is shown by +comparing the outflow in the lymphatic vessels with the normal. The +fluid exudate which has come from the blood and differs but slightly +from the blood fluid exerts not only the purely physical action of +removing and diluting injurious substances, but in many cases has a +remarkable power, exercised particularly on bacterial poisons, of +neutralizing poisons or so changing their character that they cease to +be injurious. + +We have learned, chiefly from the work of Metschnikoff, that those +white corpuscles or leucocytes which migrate from the vessels in the +greatest numbers have marked phagocytic properties, that is, they can +devour other living things and thus destroy them just as do the +amoebae. In inflammations produced by bacteria there is a very active +migration of these cells from the vessels; they accumulate in the +tissue and devour the bacteria. They may be present in such masses as +to form a dense wall around the bacteria, thus acting as a physical +bar to their further extension. The other form of amoeboid cell, which +Metschnikoff calls the macrophage, has more feeble phagocytic action +towards bacteria, and these are rarely found enclosed within them. It +is chiefly by means of their activity that other sorts of substances +are removed. They often contain dead cells or cell fragments, and when +haemorrhage takes place in a tissue they enclose and remove the +granules of blood pigment which result. They often join together, +forming connected masses, and surround such a foreign body as a hair, +or a thread which the surgeon places in a wound to close it. They may +destroy living cells, and do this seemingly when certain cells are in +too great numbers and superfluous in a part, their action tending to +restore the cell equilibrium. The foreign cells do even more than +this: they themselves may be devoured by the growing cells of the +tissue, seemingly being actuated by the same supreme idea of sacrifice +which led Buddha to give himself to the tigress. + +The explanation of most of the changes which take place in +inflammation is obvious. It is a definite property of all living +things that repair takes place after injury, and certain of the +changes are only an accentuation of those which take place in the +usual life; but others, such as the formation of the exudate, are +unusual; not only is the outpouring of fluid greatly increased, but +its character is changed. In the normal transudation[2] the substances +on which the coagulation of the blood depends pass through the vessel +wall to a very slight extent, but the exudate may contain the +coagulable material in such amounts that it easily clots. The +interchange between the fluid outside the vessels and the blood fluid +takes place by means of filtration and osmosis. There is a greater +pressure in the vessels than in the fluid outside of them, and the +fluid filters through the wall as fluid filters through a thin +membrane outside of the body. Osmosis takes place when two fluids of +different osmotic pressure are separated by animal membrane. +Difference in osmotic pressure is due to differences in molecular +concentration, the greater the number of molecules the greater is the +pressure, and the greater rapidity of flow is from the fluid of less +pressure to the fluid of greater pressure. The molecular concentration +of tissue and blood fluid is constantly being equalized by the process +of osmosis. In the injured tissue the conditions are more favorable +for the fluid of the blood to pass from the vessels: by filtration, +because owing to the dilatation of the arteries there is increased +amount of blood and greater pressure within the vessels, and the +filtering membrane is also thinner because the same amount of membrane +(here the wall of the vessel) must cover the larger surface produced +by the dilatation. It is, moreover, very generally believed that there +are minute openings in the walls of the capillaries, and these would +become larger in the dilated vessel just as openings in a sheet of +rubber become larger when this is stretched. Osmosis towards the +tissue is favored because, owing to destructive processes the +molecular pressure in the injured area is increased; an injured tissue +has been shown to take up fluid more readily outside of the body than +a corresponding uninjured tissue. The slowing of the blood stream, in +spite of the dilatation of the vessels, is due to the greater friction +of the suspended corpuscles on the walls of the vessels. This is due +to the loss from the blood of the outstreaming fluid and the relative +increase in the number of corpuscles, added to by the unevenness of +surface which the attached corpuscles produce. + +The wonderful migration of the leucocytes, which seems to show a +conscious protective action on their part, takes place under the +action of conditions which influence the movement of cells. When an +actively moving amoeba is observed it is seen that the motion is not +the result of chance, for it is influenced by conditions external to +the organism; certain substances are found to attract the amoebae +towards them and other substances to repel them. These influences or +forces affecting the movements of organisms are known as +_tropisms_, and play a large part in nature; the attraction of +various organisms towards a source of light is known as +_heliotropism_, and there are many other instances of such +attraction. The leucocytes as free moving cells also come under the +influence of such tropisms. When a small capillary tube having one end +sealed is partially filled with the bacteria which produce abscess and +placed beneath the skin it quickly becomes filled with leucocytes, +these being attracted by the bacteria it contains. Dead cells exert a +similar attraction for the large phagocytes. Such attraction is called +_chemotropism_ and is supposed to be due in the cases mentioned, +to the action of chemical substances such as are given off by the +bacteria or the dead cells. The direction of motion is due to +stimulation of that part of the body of the leucocyte which is towards +the source of the stimulus. The presence in the injured part of +bacteria or of injured and dead cells exerts an attraction for the +leucocytes within the vessels causing their migration. When the centre +of the cornea is injured, this tissue having no vessels, all the +vascular phenomena take place in the white part of the eye immediately +around the cornea, this becoming red and congested. The migration of +leucocytes from the vessels takes place chiefly on the side towards +the cornea, and the migrated cells make their way along the devious +tracts of the communicating lymph spaces to the area of injury. The +objection may be raised that it is difficult to think of a chemical +substance produced in an injured area no larger than a millimeter, +diffusing through the cornea and reaching the vessels outside this in +such quantity and concentration as to affect their contents, nor has +there been any evidence presented that definite chemical substances +are produced in injured tissues; but there is no difficulty in view of +the possibilities. It is not necessary to assume that an actual +substance so diffuses itself, but the influence exerted may be thought +of as a force, possibly some form of molecular motion, which is set in +action at the area of injury and extends from this. No actual +substance passes along a nerve when it conveys an impulse. + +We have left the injured area with an increased amount of fluid and +cells within it, with the blood vessels dilated and with both cells +and fluid streaming through their walls, and the cells belonging to +the area actively repairing damages and multiplying. The process will +continue as long as the cause which produces the injury continues to +act, and will gradually cease with the discontinuance of this action, +and this may be brought about in various ways. A foreign body may be +mechanically removed, as when a thorn is plucked out; or bacteria may +be destroyed by the leucocytes; or a poison, such as the sting of an +insect, may be diluted by the exudate until it be no longer injurious, +or it may be neutralized. Even without the removal of the cause the +power of adaptation will enable the life of the affected part to go +on, less perfectly perhaps, in the new environment. The excess of +fluid is removed by the outflow exceeding the inflow, or it may pass +to some one of the surfaces of the body, or in other cases an incision +favors its escape. The excess of cells is in part removed with the +fluid, in part they disappear by undergoing solution and in part they +are devoured by other cells. With the diminishing cell activity the +blood vessels resume their usual calibre, and when the newly formed +vessels become redundant they disappear by undergoing atrophy in the +same way as other tissues which have become useless. + +When these changes take place rapidly the inflammation is said to be +acute, and chronic when they take place slowly. Chronic inflammation +is more complex than is the acute, and there is more variation in the +single conditions. The chronicity may be due to a number of +conditions, as the persistence of a cause, or to incompleteness of +repair which renders the part once affected more vulnerable, to such a +degree even that the ordinary conditions to which it is subjected +become injurious. A chronic inflammation may be little more than an +almost continuous series of acute inflammations, with repair +continuously less perfect. Chronic imflammations are a prerogative of +the old as compared with the young, of the weak rather than the +strong. + +FOOTNOTES: +[1] The term exudation is used to designate the +passing of cells and fluid from the vessels in inflammation; the +material is the exudate. + +[2] By transudation is meant the constant interchange between +the blood and the tissue fluid. + + + + +CHAPTER V + +INFECTIOUS DISEASES.--THE HISTORICAL IMPORTANCE OF EPIDEMICS OF +DISEASE.--THE LOSSES IN BATTLE CONTRASTED WITH THE LOSSES IN ARMIES +PRODUCED BY--INFECTIOUS DISEASES.--THE DEVELOPMENT OF KNOWLEDGE OF +EPIDEMICS.--THE VIEWS OF HIPPOCRATES AND ARISTOTLE.--SPORADIC AND +EPIDEMIC DISEASES.--THE THEORY OF THE EPIDEMIC CONSTITUTION.--THEORY +THAT THE CONTAGIOUS MATERIAL IS LIVING.--THE DISCOVERY OF BACTERIA BY +LOEWENHOECK IN 1675.--THE RELATION OF CONTAGION TO THE THEORY OF +SPONTANEOUS GENERATION.--NEEDHAM AND SPALLANZANI.--THE DISCOVERY OF +THE COMPOUND MICROSCOPE IN 1605.--THE PROOF THAT A LIVING ORGANISM IS +THE CAUSE OF A DISEASE.--ANTHRAX.--THE DISCOVERY OF THE ANTHRAX +BACILLUS IN 1851.--THE CULTIVATION OF THE BACILLUS BY KOCH.--THE MODE +OF INFECTION.--THE WORK OF PASTEUR ON ANTHRAX.--THE IMPORTANCE OF THE +DISEASE. + + +These are diseases which are caused by living things which enter the +tissues of the body and, living at the expense of the body, produce +injury. Such diseases play an important part in the life of man; the +majority of deaths are caused directly or indirectly by infection. No +other diseases have been so much studied, and in no other department +of science has knowledge been capable of such direct application in +promoting the health, the efficiency and the happiness of man. This +knowledge has added years to the average length of life, it has +rendered possible such great engineering works as the Panama Canal, +and has contributed to the food supply by making habitation possible +over large and productive regions of the earth, formerly uninhabitable +owing to the prevalence of disease. It is not too much to say that our +modern civilization is dependent upon this knowledge. The massing of +the people in large cities, the factory life, the much greater social +life, which are all prominent features of modern civilization, would +be difficult or impossible without control of the infectious diseases. +The rapidity of communication and the increased general movement of +people, which have developed in equal ratio with the massing, would +serve to extend widely every local outbreak of infection. The +principles underlying fermentation and putrefaction which have been +applied with great economic advantage to the preservation of food were +many of them developed in the course of the study of the infectious +diseases. Whether the development of the present civilization is for +the ultimate advantage of man may perhaps be disputed, but medicine +has made it possible. + +The infectious diseases appearing in the form of great epidemics have +been important factors in determining historical events, for they have +led to the defeat of armies, the fall of cities and of nations. War is +properly regarded as one of the greatest evils that can afflict a +nation, since it destroys men in the bloom of youth, at the age of +greatest service, and brings sorrow and care and poverty to many. But +the most potent factor in the losses of war is not the deaths in +battle but the deaths from disease. If we designate the lives lost in +battle, the killed and the wounded who die, as 1, the loss of the +German army from disease in 1870-71 was 1.5, that of the Russians in +1877-78 was 2.7, that of the French in Mexico was 2.8, that of the +French in the Crimea 3.7, that of the English in Egypt 4.2. The total +loss of the German army in 1870-71 from wounds and disease was 43,182 +officers and men, and this seems a small number compared with the +129,128 deaths from smallpox in the same period in Prussia alone. In +the Spanish American war there were 20,178 cases of typhoid fever with +1,580 deaths. In the South African war there were in the British +troops 31,118 cases of typhoid with 5,877 deaths, and 5,149 deaths +from other diseases while the loss in battle was 7,582. The Athenian +plague which prevailed during the Peloponnesian war, 431-405 B.C., not +only caused the death of Pericles, but according to Thucydides a loss +of 4,800 Athenian soldiers, and brought about the downfall of the +Athenian hegemony in Greece. In the Crimean war between 1853-56, +16,000 English, 80,000 French and 800,000 Russians died of typhus +fever. The plague contributed as much as did the arms of the Turks to +the downfall of Constantinople and the Eastern Empire in 1453. It was +the plague which in 1348 overthrew Siena from her proud position as +one of the first of the Italian cities and the rival of Florence, and +broke the city forever, leaving it as a phantom of its former glory +and prosperity. The work on the great cathedral which had progressed +for ten years was suspended, and when it was resumed it was upon a +scale adjusted to the diminished wealth of the city, and the plan +restricted to the present dimensions. As a little relief to the +darkness the same plague saw the birth of the novel in the tales of +Boccaccio, which were related to a delighted audience of the women who +had fled from the plague in Florence to a rural retreat. + +The knowledge which has come from the study of infectious disease has +served also to broaden our conception of disease and has created +preventive medicine; it has linked more closely to medicine such +sciences as zooelogy and botany; it has given birth to the sciences of +bacteriology and protozooelogy and in a way has brought all sciences +more closely together. Above all it has made medicine scientific, and +never has knowledge obtained been more quickening and stimulating to +its pursuit. + +Although the dimensions of this book forbid much reference to the +historical development of a subject, some mention must still be made +of the development of knowledge of the infectious diseases. It was +early recognized that there were diseases which differed in character +from those generally prevalent; large numbers of people were affected +in the same way; the disease beginning with a few cases gradually +increased in intensity until an acme was reached which prevailed for a +time and the disease gradually disappeared. Such diseases were +attributed to changes in the air, to the influence of planets or to +the action of offended gods. The priests and charlatans who sought to +excuse their inability to treat epidemics successfully were quick to +affirm supernatural causes. Hippocrates (400 B.C.), with whom medicine +may be said to begin, thought such diseases, even then called +epidemics, were caused by the air; he says, "When many individuals are +attacked by a disease at the same time, the cause must be sought in +some agent which is common to all, something which everyone uses, and +that is the air which must contain at this time something injurious." +Aristotle recognized that disease was often conveyed by contact, and +Varro (116-27 B.C.) advanced the idea that disease might be caused by +minute organisms. He says, "Certain minute organisms develop which the +eye cannot see, and which being disseminated in the air enter into the +body by means of the mouth and nostrils and give rise to serious +ailments." In spite of this hypothesis, which has proved to be +correct, the belief became general that epidemics were due to +putrefaction of the air brought about by decaying animal bodies, (this +explaining the frequent association of epidemics and wars,) by +emanations from swamps, by periods of unusual heat, etc. + +With the continued study of epidemics the importance of contagion was +recognized; it was found that epidemics differed in character and in +the modes of extension. Some seemed to extend by contact with the +sick, and in others this seemed to play no part; it was further found +impossible in many cases to show evidence of air contamination, and +contamination of the air by putrefactive material did not always +produce disease. Most important was the recognition that single cases +of diseases which often occurred in epidemic form might be present and +no further extension follow; this led to the assumption in epidemics +of the existence of some condition in addition to the cause, and which +made the cause operative. In this way arose the theory of the epidemic +constitution, a supposed peculiar condition of the body due to changes +in the character of the air, or to the climate, or to changes in the +interior of the earth as shown by earthquakes, or to the movements of +planets; in consequence of this peculiar constitution there was a +greater susceptibility to disease, but the direct cause might arise in +the interior of the body or enter the body from without. The character +of the disease which appeared in epidemic form, the "Genius +epidemicus," was determined not by differences in the intrinsic cause, +but by the type of constitution which prevailed at that time. The +first epidemic of cholera which visited Europe in 1830-37 was for the +most part referred to the existence of a peculiar epidemic +constitution for which various causes were assigned. It was only when +the second epidemic of this disease appeared in 1840 that the +existence of some special virus or poison which entered the body was +assumed. + +Meanwhile, by the study of the material of disease knowledge was being +slowly acquired which had much bearing on the causes. The first +observations which tended to show that the causes were living were +made by a learned Jesuit, Athanasius, in 1659. He found in milk, +cheese, vinegar, decayed vegetables, and in the blood and secretions +of cases of plague bodies, which he described as tiny worms and which +he thought were due to putrefaction. He studied these objects with the +simple lenses in use at that time, and there is little doubt that he +did see certain of the larger organisms which are present in vinegar, +cheese and decaying vegetables, and it is not impossible that he may +have seen the animal and vegetable cells. + +The first description of bacteria with illustrations showing their +forms was given by Loewenhoeck, a linen dealer in Amsterdam in 1675. +The fineness of the linen being determined by the number of threads in +a given area, it is necessary to examine it with a magnifying lens, +and he succeeded in perfecting a simple lens with which objects +smaller than had been seen up to that time became visible. It must be +added that he was probably endowed with very unusual acuteness of +vision. He found in a drop of water, in the fluid in the intestines of +frogs and birds, and in his evacuations, objects of great minuteness +which differed from each other in form and size and in the peculiar +motion which some of them possessed. In the year 1683 he presented to +the Royal Society of London a paper describing a certain minute +organism which he found in the tartar of his teeth. After these +observations of Loewenhoeck became known to the world they quickly +found application in disease, although the author had expressed +himself very cautiously in this regard. The strongest exponent of the +view of a living contagion was Plenciz, 1762, a physician of Vienna, +basing his belief not only on the demonstration of minute organisms by +Loewenhoeck which he was able to verify, but on certain shrewdly +conceived theoretical considerations. He was the first to recognize +the specificity of the epidemic diseases, and argued from this that +each disease must have a specific cause. "Just as a certain plant +comes from the seed of the same plant and not from any plant at will, +so each contagious disease must be propagated from a similar disease +and cannot be the result of any other disease." Further he says, "It +is necessary to assume that during the prevalence of an epidemic the +contagious material undergoes an enormous increase, and this is +compatible only with the assumption that it is a living substance." +But as is so often the case, speculation ran far ahead of the +observations on which it is based. There was a long gap between the +observations of Loewenhoeck and the theories of Plenciz, justified as +these have been by present knowledge. In the spirit of speculation +which was dominant in Europe and particularly in Germany in the latter +half of the eighteenth and the first half of the nineteenth centuries, +hypotheses did not stimulate research, but led to further +speculations. As late as 1820 Ozanam expressed himself as follows: +"Many authors have written concerning the animal nature of the +contagion of disease; many have assumed it to be developed from animal +substance, and that it is itself animal and possesses the property of +life. I shall not waste time in refuting these absurd hypotheses." The +theory of a living contagion was too simple, and not sufficiently +related to the problems of the universe to serve the medical +philosophers. + +Knowledge of the minute organisms was slowly accumulating. The first +questions to be determined were as to their nature and origin. How +were they produced? Did they come from bodies of the same sort +according to the general laws governing the production of living +things, or did they arise spontaneously? a question which could not be +solved by speculation but by experiment. The first experiments, by +Needham, 1745, pointed to the spontaneous origin of the organisms. He +enclosed various substances in carefully sealed watch crystals from +which the air was excluded, and found that animalculi appeared in the +substance, and argued from this that they developed spontaneously. In +1769, Spallanzani, a skilled experimental physiologist, in a brilliant +series of experiments showed the imperfect character of Needham's work +and the fallacy of his conclusions. Spallanzani placed fluids, which +easily became putrid, in glass tubes, which he then hermetically +sealed and boiled. He found that the fluid remained clear and +unchanged; if, however, he broke the sealed point of such a tube and +allowed the air to enter, putrefaction, or in some cases fermentation, +of the contents took place. He concluded that boiling the substances +destroyed the living germs which they contained, the sealed tubes +prevented the air from entering, and when putrefaction or fermentation +of the contents took place the organisms to which this was due, being +contained in the air, entered from without. Objection was made to the +conclusions of Spallanzani that heating the air in the closed tubes so +changed its character as to prevent development of organisms in the +contents. This objection was finally set aside by Pasteur, who showed +that it was not necessary to seal the end of the tube before boiling, +but it could be closed by a plug of cotton wool, which mechanically +removed the organisms from the air which entered the tube, or if the +tube were bent in the shape of a _U_ and the end left open, +organisms from the air could not pass into the tube against gravity +when air movement within the tube was prevented by bending. The +possibility of spontaneous generation cannot be denied, but that it +takes place is against all human experience. + +It was not possible to attain any considerable knowledge of the +bacteria discovered by Loewenhoeck until more perfect instruments for +studying them were devised. Lenses for studying objects were used in +remote antiquity, but the compound microscope in which the image made +by the lens is further magnified was not discovered until 1605, and +when first made was so imperfect that the best simple lenses gave +clearer definition. With the betterment of the microscope, increasing +the magnifying power and the sharpness of the image of the object +seen, it became possible to classify the minute organisms according to +size and form and to study the separate species. The microscope has +now reached such a degree of perfection that objects smaller than one +one hundred thousandth of an inch in diameter can be clearly seen and +photographed. + +Great impetus was given to the biological investigation of disease by +the discoveries which led to the formulation of the cell theory in +1840 and the brilliant work of Pasteur on fermentation,[1] but it was +not until 1878 that it was definitely proved that a disease of cattle +called anthrax was due to a species of bacteria. What should be +regarded as such proof had been formulated by Henle in 1840. To prove +that a certain sort of organism when found associated with a disease +is the cause of the disease, three things are necessary: + +1. The organism must always be found in the diseased animal and +associated with the changes produced by the disease. + +2. The organism so found must be grown outside of the body in what is +termed pure cultures, that is, not associated with any other +organisms, and for so long a time with constant transfers or new +seedings that there can be no admixture of other products of the +disease in the material in which it is grown. + +3. The disease must be produced by inoculating a susceptible animal +with a small portion of such a culture, and the organism shown in +relation to the lesions so produced. + +It is worth while to devote some attention to the disease anthrax. +This occupies a unique position, in that it was the first of the +infectious diseases to be scientifically investigated. In this +investigation one fact after another was discovered and confirmed; +some of these facts seemed to give clearer conceptions of the disease, +others served to make it more obscure; new questions arose with each +extension of knowledge; in the course of the work new methods of +investigation were discovered; the sides of the arch were slowly and +painfully erected by the work of many men, and finally one man placed +the keystone and anthrax was for a long time the best known of +diseases. Men whose reputation is now worldwide first became known by +their work in this disease. It was a favorable disease for +investigation, being a disease primarily of cattle, but occasionally +appearing in man, and the susceptibility of laboratory animals made +possible experimental study. + +Anthrax is a disease of domestic cattle affecting particularly bovine +cattle, horses and sheep, swine more rarely. The disease exists in +practically all countries and has caused great economic losses. There +are no characteristic symptoms of the disease; the affected cattle +have high fever, refuse to eat, their pulse and respiration are rapid, +they become progressively weaker, unable to walk and finally fall. The +disease lasts a variable time; in the most acute cases animals may die +in less than twenty-four hours, or the disease may last ten or +fourteen days; recovery from the disease is rare and treatment has no +effect. It does not appear in the form of epidemics, but single cases +appear frequently or rarely, and there is seemingly no extension from +case to case, animals in adjoining stalls to the sick are not more +prone to infection than others of the herd. On examination after death +the blood is dark and fluid, the spleen is greatly enlarged (one of +the names of the disease "splenic fever" indicates the relation to the +spleen) and there is often bloody fluid in the tissues. + +Where the disease is prevalent there are numbers of human cases. Only +those become infected who come into close relations with cattle, the +infection most commonly taking place from small wounds or scratches +made in skinning dead cattle or in handling hides. The wool of sheep +who die of the disease finds its way into commerce, and those employed +in handling the wool have a form of anthrax known as wool-sorters' +disease in which lesions are found in the lungs, the organisms being +mingled with the wool dust and inspired. In Boston occasional cases of +anthrax appear in teamsters who are employed in handling and carrying +hides. The disease in man is not so fatal as in cattle, for it remains +local for a time at the site of infection, and this local disease can +be successfully treated. + +The beginning of our knowledge of the cause dates from 1851, when +small rod-shaped bodies (Fig. 17) were found in the blood of the +affected cattle, and by the work of a number of observers it was +established that these bodies were constantly present. Nothing was +known of their nature; some held that they were living organisms, +others that they were formed in the body as a result of the disease. +Next the causal relation of these bodies with the disease was shown +and in several ways. The disease could be caused in other cattle by +injecting blood containing the rods beneath the skin, certainly no +proof, for the blood might have contained in addition to the rods +something which was the real cause of the disease. Next it was shown +that the blood of the unborn calf of a cow who died of the disease did +not contain the rods, and the disease could not be produced by +inoculating with the calf's blood although the blood of the mother was +infectious. This was a very strong indication that the rods were the +cause; the maternal and foetal blood are separated by a membrane +through which fluids and substances in solution pass; but insoluble +substances, even when very minutely subdivided, do not pass the +membrane. If the cause were a poison in solution, the foetal blood +would have been as toxic as the maternal. The blood of infected cattle +was filtered through filters made of unbaked porcelain and having very +fine pores which allowed only the blood fluid to pass, holding back +both the blood corpuscles and the rods, and such filtered blood was +found to be innocuous. It was further shown that the rods increased +enormously in number in the infected animal, for the blood contained +them in great numbers when but a fraction of a drop was used for +inoculation. Attempts were also made with a greater or less degree of +success to grow the rod shaped organisms or bacilli in various fluids, +and the characteristic disease was produced by inoculating animals +with these cultures; but it remained for Koch, 1878, who was at that +time an obscure young country physician, to show the life history of +the organism and to clear up the obscurity of the disease. Up to that +time, although it had been shown that the rods or bacilli contained in +the blood were living organisms and the cause of the disease, this did +not explain the mode of infection; how the organisms contained in the +blood passed to another animal, why the disease occurred on certain +farms and the adjoining farms, particularly if they lay higher, were +free. Koch showed that in the cultures the organisms grew out into +long interlacing threads, and that in these threads spores which were +very difficult to destroy developed at intervals; that the organisms +grew easily in bouillon, in milk, in blood, and even in an infusion of +hay made by soaking this in water. This explained, what had been an +enigma before, how the fields became sources of infection. The +infection did not spread from animal to animal by contact, but +infection took place from eating grass or hay which contained either +the bacilli or their spores. When a dead animal was skinned on the +field, the bacilli contained in the blood escaped and became mingled +with the various fluids which flowed from the body and in which they +grew and developed spores. It was shown by Pasteur that even when a +carcass was buried the earthworms brought spores developed in the body +to the surface and deposited them in their casts, and in this way also +the fields became infected. From such a spot of infected earth the +spores could be washed by the rains over greater areas and would find +opportunity to develop further and form new spores in puddles of water +left on the fields, which became a culture medium by the soaking of +the dead grass. The contamination of the fields was also brought about +by spreading over them the accumulations of stable manure which +contained the discharges of the sick cattle. The tendency of the +disease to extend to lower-lying adjacent fields was due to the spores +being washed from the upper fields to the lower by the spring +freshets. Meanwhile Pasteur had discovered that by growing the +organisms at higher temperatures than the animal body, it was possible +to attenuate the virulence of the bacilli so that inoculations with +these produced a mild form of the disease which rendered the +inoculated animals immune to the fatal disease. The description of +Pasteur's work on the disease as given in the account of his life by +his son-in-law is fascinating. + +Hides and wool taken from dead animals invariably contained the spores +which could pass unharmed through some of the curing processes, and +were responsible for some of the cases in man. Owing to the +introduction of regulations which were based on the knowledge of the +cause of the disease and the life history of the organism, together +with the prophylactic inoculation devised by Pasteur, the incidence of +the disease has been very greatly lessened. Looking at the matter from +the lowest point of view, the money which has been saved by the +control of the disease, as shown in its decline, has been many times +the cost of all the work of the investigations which made the control +possible. It is a greater satisfaction to know that many human lives +have been saved, and that small farmers and shepherds have been the +chief sharers in the economic benefits. The indirect benefits, +however, which have resulted from the application of the knowledge of +this disease, and the methods of investigation developed here, to the +study of the infections more peculiar to man, are very much greater. + +FOOTNOTE: +[1] The interesting analogy between fermentation and infectious +disease did not escape attention. A clear fluid containing in solution +sugar and other constituents necessary for the life of the yeast cells +will remain clear provided all living things within it have been +destroyed and those in the air prevented from entering. If it be +inoculated with a minute fragment of yeast culture containing a few +yeast cells, for a time no change takes place; but gradually the fluid +becomes cloudy, bubbles of gas appear in it and its taste changes. +Finally it again becomes clear, a sediment forms at the bottom, and on +re-inoculating it with yeast culture no fermentation takes place. The +analogy is obvious, the fluid in the first instance corresponds with +an individual susceptible to the disease, the inoculated yeast to the +contagion from a case of transmissible disease, the fermentation to +the illness with fever, etc., which constitutes the disease, the +returning clearness of the fluid to the recovery, and like the +fermenting fluid the individual is not susceptible to a new attack of +the disease. It will be observed that during the process both the +yeast and the material which produced the disease have enormously +increased. Fermentation of immense quantities of fluid could be +produced by the sediment of yeast cells at the bottom of the vessel +and a single case of smallpox would be capable of infecting +multitudes. + + + + +CHAPTER VI + +CLASSIFICATION OF THE ORGANISMS WHICH CAUSE DISEASE.--BACTERIA: SIZE, +SHAPE, STRUCTURE, CAPACITY FOR GROWTH, MULTIPLICATION AND SPORE +FORMATION.--THE ARTIFICIAL CULTIVATION OF BACTERIA.--THE IMPORTANCE OF +BACTERIA IN NATURE.--VARIATIONS IN BACTERIA.--SAPROPHYTIC AND +PARASITIC FORMS.--PROTOZOA.--STRUCTURE MORE COMPLICATED THAN THAT OF +BACTERIA.--DISTRIBUTION IN NATURE.--GROWTH AND MULTIPLICATION.-- +CONJUGATION AND SEXUAL REPRODUCTION.--SPORE FORMATION.--THE NECESSITY +FOR A FLUID ENVIRONMENT.--THE FOOD OF PROTOZOA.--PARASITISM.--THE +ULTRA-MICROSCOPIC OR FILTERABLE--ORGANISMS.--THE LIMITATION OF THE +MICROSCOPE.--PORCELAIN FILTERS TO SEPARATE ORGANISMS FROM A FLUID.-- +FOOT AND MOUTH DISEASE PRODUCED BY AN ULTRA-MICROSCOPIC ORGANISM.-- +OTHER DISEASES SO PRODUCED.--DO NEW DISEASES APPEAR? + + +The living organisms which cause the infectious diseases are +classified under bacteria, protozoa, yeasts, moulds, and +ultra-microscopic organisms. It is necessary to place in a separate +class the organisms whose existence is known, but which are not +visible under the highest powers of the microscope, and have not been +classified. The yeasts and moulds play a minor part in the production +of disease and cannot be considered in the necessary limitation of +space. + +[Illustration: FIG. 17.--VARIOUS FORMS OF BACTERIA, _a_, _b_, _c_, +_d_, Round bacteria or cocci: (_a_) Staphylococci, organisms which +occur in groups and a common cause of boils; (_b_) streptococci, +organisms which occur in chains and produce erysipelas and more severe +forms of inflammation; (_c_) diplococci, or paired organisms with a +capsule, which cause acute pneumonia; (_d_) gonococci, with the +opposed surfaces flattened, which cause gonorrhoea. _e_, _f_, _g_, +_h_, Rod-shaped bacteria or bacilli: (_e_) diphtheria bacilli; (_f_) +tubercle bacilli; (_g_) anthrax bacilli; (_h_) the same bacilli in +cultures and producing spores; a small group of spores is shown. (_i_) +Cholera spirillae. (_j_) Typhoid bacilli. (_k_) Tetanus bacillus; +_i_, _j_, _k_ are actively motile, motion being effected by the small +attached threads. (_l_) The screw-shaped spirochite which is the cause +of syphilis.] + +The bacteria (Fig. 17) are unicellular organisms and vary greatly in +size, shape and capacity of growth. The smallest of the pathogenic or +disease-producing bacteria is the influenza bacillus, 1/51000 of an +inch in length and 1/102000 of an inch in thickness; and among the +largest is a bacillus causing an animal disease which is 1/2000 of an +inch in length and 1/25000 of an inch in diameter. Among the +free-living non-pathogenic forms much larger examples are found. In +shape bacteria are round, or rod-shaped, or spiral; the round forms +are called micrococci, the rod-shaped bacilli and the spiral forms are +called spirilli. A clearer idea of the size is possibly given by the +calculation that a drop of water would contain one billion micrococci +of the usual size. Their structure in a general way conforms with that +of other cells. On the outside is a cell membrane which encloses +cytoplasm and nucleus; the latter, however, is not in a single mass, +but the nuclear material is distributed through the cell. Many of the +bacteria have the power of motion, this being effected by small +hair-like appendages or flagellae which may be numerous, projecting +from all parts of the organisms or from one or both ends, the movement +being produced by rapid lashing of these hairs. A bacterium grows +until it attains the size of the species, when it divides by simple +cleavage at right angles to the long axis forming two individuals. In +some of the spherical forms division takes place alternately in two +planes, and not infrequently the single individuals adhere, forming +figures of long threads or chains or double forms. The rate of growth +varies with the species and with the environment, and under the best +conditions may be very rapid. A generation, that is, the interval +between divisions, has been seen to take place in twenty minutes. At +this rate of growth from a single cholera bacillus sixteen quadrillion +might arise in a single day. Such a rate of growth is extremely +improbable under either natural or artificial conditions, both from +lack of food and from the accumulation in the fluid of waste products +which check growth. Many species of bacteria in addition to this +simple mode of multiplication form spores which are in a way analogous +to the seeds of higher plants and are much more resistant than the +simple or vegetative forms; they endure boiling water and even higher +degrees of dry heat for a considerable time before they are destroyed. +When these spores are placed in conditions favorable for bacterial +life, the bacterial cells grow out from them and the usual mode of +multiplication continues. This capacity for spore formation is of +great importance, and until it was discovered by Cohn in 1876, many of +the conditions of disease and putrefaction could not be explained. +Spores, as the seeds of plants, often seem to be produced when the +conditions are unfavorable; the bacterium then changes into this form, +which under natural conditions is almost indestructible and awaits +better days. + +The bacteria are divided into species, the classification being based +on their forms, on the mode of growth, the various substances which +they produce and their capacity for producing disease. The +differentiation of species in bacteria is based chiefly upon their +properties, there being too little difference in form and size to +distinguish species. The introduction of methods of culture was +followed by an immediate advance of our knowledge concerning them. +This method consists in the use of fluid and solid substances which +contain the necessary salts and other ingredients for their food, and +in or on which they are planted. The use of a solid or gelatinous +medium for growth has greatly facilitated the separation of single +species from a mixture of bacteria; a culture fluid containing +sufficient gelatine to render it solid when cooled is sown with the +bacteria to be tested by placing in it while warm and fluid, a small +portion of material containing the bacteria, and after being +thoroughly mixed the fluid is poured on a glass plate and allowed to +cool. The bacteria are in this way separated, and each by its growth +forms a single colony which can be further tested. It is self-evident +that all culture material must be sterilized by heat before using, and +in the manipulations care must be exercised to avoid contamination +from the air. The refraction index of the bacterial cell is so slight +that the microscopic study is facilitated or made possible by staining +them with various aniline dyes. Owing to differences in the cell +material the different species of bacteria show differences in the +facility with which they take the color and the tenacity with which +they retain it, and this also forms a means of species differentiation. +The interrelation of science is well shown in this, for it was the +discovery of the aniline dyes in the latter half of the nineteenth +century which made the fruitful study of bacteria possible. + +From the simplicity of structure it is not improbable that the +bacteria are among the oldest forms of life, and all life has become +adapted to their presence. They are of universal distribution; they +play such an important part in the inter-relations of living things +that it is probable life could not continue without them, at least not +in the present way. They form important food for other unicellular +organisms which are important links in the chain; they are the agents +of decomposition, by which the complex substances of living things are +reduced to elementary substances and made available for use; without +them plant life would be impossible, for it is by their +instrumentality that material in the soil is so changed as to be +available as plant food; by their action many of the important foods +of man, often those especially delectable, are produced; they are +constantly with us on all the surfaces of the body; masses live on the +intestinal surfaces and the excrement is largely composed of bacteria. +It has been said that life would be impossible without bacteria, for +the accumulation of the carcasses of all animals which have died would +so encumber the earth as to prevent its use; but the folly of such +speculation is shown by the fact that animals would not have been +there without bacteria. It has been shown, however, that the presence +of bacteria in the intestine of the higher animals is not essential +for life. The coldest parts of the ocean are free from those forms +which live in the intestines, and fish and birds inhabiting these +regions have been found free from bacteria; it has also been found +possible to remove small animals from their mother by Caesarian section +and to rear them for a few weeks on sterilized food, showing that +digestion and nutrition may go on without bacteria. + +Certain species of bacteria are aerobic, that is, they need free +oxygen for their growth; others are anaerobic and will not grow in the +presence of oxygen. Most of the bacteria which produce disease are +facultative, that is, they grow either with or without oxygen; but +certain of them, as the bacillus of tetanus, are anaerobic. There is, +of course, abundance of oxygen in the blood and tissues, but it is so +combined as to be unavailable for the bacteria. Bacteria may further +be divided into those which are saprophytic or which find favorable +conditions for life outside of the body, and the parasitic. Many are +exclusively parasitic or saprophytic, and many are facultative, both +conditions of living being possible. It has been found possible by +varying in many ways the character of the culture medium and +temperature to grow under artificial conditions outside of the body +most, if not all, of the bacteria which cause disease. Thus, such +bacteria as tubercle bacilli and the influenza bacillus can be +cultivated, but they certainly would not find natural conditions which +would make saprophytic growth possible. + +Bacteria may be very sensitive to the presence of certain substances +in the fluid in which they are growing. Growth may be inhibited by the +smallest trace of some of the metallic salts, as corrosive sublimate, +although the bacteria themselves are not destroyed. If small pieces of +gold foil be placed on the surface of prepared jelly on which bacteria +have been planted, no growth will take place in the vicinity of the +gold foil. + +Variations can easily be produced in bacteria, but they do not tend to +become established. In certain of the bacterial species there are +strains which represent slight variations from the type but which are +not sufficient to constitute new species. If the environment in which +bacteria are living be unusual and to a greater or less degree +unfavorable, those individuals in the mass with the least power of +adaptibility will perish, those more resistant and with greater +adaptability will survive and propagate; and the peculiarity being +transmitted a new strain will arise characterized by this +adaptability. Bacteria with slight adaptability to the environment of +the tissues and fluids of the animal body can, by repeated +inoculations, become so adapted to the new environment as to be in a +high degree pathogenic. In such a process the organisms with the least +power of adaptation are destroyed and new generations are formed from +those of greater power of adaptation. When bacteria are caused to grow +in a new environment they may acquire new characteristics. The anthrax +bacilli find the optimum conditions for growth at the temperature of +the animal body, but they will grow at temperatures both above and +below this. Pasteur found that by gradually increasing the temperature +they could be grown at one hundred and ten degrees. When grown at this +temperature they were no longer so virulent and produced in animals a +mild non-fatal form of anthrax which protected the animal when +inoculated with the virulent strain. The well known variations in the +character of disease, shown in differences in severity and ease of +transmission, seen in different years and in different epidemics, may +be due to many conditions, but probably variation in the infecting +organisms is the most important. + +The protozoa, like the bacteria, are unicellular organisms and contain +a nucleus as do all cells. They vary in size from forms seen with +difficulty under the highest power of the microscope to forms readily +seen with the unaided eye. Their structure in general is more complex +than is the structure of bacteria, and many show extreme +differentiation of parts of the single cells, as a firm exterior +surface or cuticle, an internal skeleton, organs of locomotion, mouth +and digestive organs and organs of excretion. They are more widely +distributed than are the bacteria, and found from pole to pole in all +oceans and in all fresh water. There are many modes of multiplication, +and these are often extremely complicated. The most general mode and +one which is common to all is by simple division; a modification of +this is by budding in which projections or buds form on the body and +after separation become new organisms. In other cases spores form +within the cell which become free and develop further into complete +organisms. These simple modes of multiplication often alternate in the +same organism with sexual differentiation and conjugation. There is +never a permanent sexual differentiation, but the sexual forms develop +from a simple and non-sexual organism. Usually the sexual forms +develop only in a special environment; thus the protozoon which in man +is the cause of malaria, multiplies in the human blood by simple +division, but in the body of the mosquito multiplication by sexual +differentiation takes place. Under no conditions is multiplication so +rapid as with the bacteria, and in general the simpler the form of +organism the more rapid is the multiplication. It is common to all of +the protozoa to develop forms which have great powers of resistance, +this being due in some cases to encystment, in which condition a +resistant membrane is formed on the outside, in others to the +production of spores. A fluid environment is essential to the life of +the protozoa, but the resistant forms can endure long periods of +dryness or other unfavorable environmental conditions. The universal +distribution of the protozoa is due to this; the spores or cysts can +be carried long distances by the wind and develop into active forms +when they reach an environment which is favorable. Their distribution +in water depends upon the amount of organic material this contains. In +pure drinking water there may be very few, but in stagnant water they +are very numerous, living not on the organic material in solution in +this, but on the bacteria which find in such fluid favorable +conditions for existence. The food of protozoa consists chiefly of +other organisms, particularly bacteria, and they are classed with the +animals. The protozoa are the most widely distributed and the most +universal of the parasites. The infectious diseases which they produce +in man, although among the most serious are less in number than those +produced by bacteria. So marked is the tendency to parasitism that +they are often parasitic for each other, smaller forms entering into +and living upon the larger. Variation does not seem to be so marked in +the protozoa as in the bacteria, though this is possibly due to our +greater ignorance of them as a class. We are not able, except in rare +instances, to grow them in pure culture, and study innumerable +generations under changes in the environment, as the bacteria have +been studied. + +If we regard the living things on earth from the narrow point of view +as to whether they are necessary or useless or hostile to man, the +protozoa must be regarded as about the least useful members of the +biological society. It is very possible that such a conclusion is due +to ignorance; so closely are all living things united, so dependent is +one form of cell activity upon other forms that it is impossible to +foretell the result of the removal of a link. The protozoa do not seem +to be as necessary for the life of man as are the bacteria; they +produce many of the diseases of man, many of the diseases of animals +on which man depends for food; they cause great destruction in plant +life, and in the soil they feed upon the useful bacteria. It is well +to remember, however, that fifty years ago several of the organs of +the body whose activity we now recognize as furnishing substances +necessary for life were regarded as useless members and, since they +became the seat of tumors, as dangerous members of the body. The only +organ which now seems to come into such a class is the vermiform +appendix, and its lowly position among organs is due merely to an +unhappy accident of development. + +The class of organisms known as the filterable viruses or the +ultra-microscopic or the invisible organisms have a special interest +in many ways. The limitation in the power of the microscope for the +study of minute objects is due not to a defect in the instrument but +to the length of the wave of light. It is impossible to see clearly +under the microscope using white light, objects which are smaller in +diameter than the length of the wave which gives a limit of 0.5 mu. or +1/125,000 of an inch. By using waves of shorter length, as the +ultra-violet light, objects of 0.1 mu. or 1/250000 of an inch can be +seen; but as these methods depend upon photography for the +demonstration of the object the study is difficult. The presence of +objects still smaller than 0.1 m. can be detected in a fluid by the +use of the dark field illumination and the ultra-microscope, the +principle of which is the direction of a powerful oblique ray of light +into the field of the microscope. The objects are not visible as such, +but the dispersion of the light by their presence is seen. + +The demonstration that infectious diseases were produced by organisms +so small as to be beyond demonstration with the best microscopes was +made possible by showing, that some fluid from a diseased animal was +infectious; and capable of producing the disease when inoculated into +a susceptible animal. The fluid was then filtered through porcelain +filters which were known to hold back all objects of the size of the +smallest bacteria and the disease produced by inoculating with the +clear filtrate. There are a number of such filters of different +degrees of porosity manufactured, and they are often used to procure +pure water for drinking, for which use they are more or less, +generally however, less efficacious. The filter has the form of a +hollow cylinder and the liquid to be filtered is forced through it +under pressure. For domestic use the filter is attached by its open +end to the water tap and the pressure from the mains forces the water +through it. In laboratory uses, denser filters of smaller diameters +are used, and the filter is surrounded by the fluid to be tested. The +open end of the filter passes into a vessel from which the air is +exhausted and filtration takes place from without inward. The test of +the effectiveness of the filter is made by adding to the filtering +fluid some very minute and easily recognizable bacteria and testing +the filtrate for their presence. These filters have been studied +microscopically by grinding very thin sections and measuring the +diameter of the spaces in the material. These are very numerous, and +from 1/25000 to 1/1000 of an inch in diameter, spaces which would +allow bacteria to pass through, but they are held back by the very +fine openings between the spaces and by the tortuosity of the +intercommunications. When the coarser of such filters have been long +in domestic service in filtering drinking water, bacteria may grow in +and through them giving greater bacterial content to the supposed +bacteria-free filtrate than in the filtering water. + +That an animal disease was due to such a minute and filterable +organism was first shown by Loeffler in 1898 for the foot and mouth +disease of cattle. This is one of the most infectious and easily +communicable diseases. The lesions of the disease take the form of +blisters which form on the lips and feet and in the mouths of cattle, +and inoculation with minute quantities of the fluid in the blisters +produces the disease. Loeffler filtered the fluid through porcelain +filters, hoping to obtain a material which inoculated into other +cattle would render them immune, and to his surprise found that the +typical disease was produced by inoculating with the filtrate. +Naturally the first idea was that the disease was caused by some +soluble poison and not by a living organism, but this was disproved in +a number of ways. The most powerful poison known is obtained from +cultures of the tetanus bacillus of which 0.000,000,1 of a gram (one +gram is 15.43 grains) kills a mouse, or one gram kills ten million +mice. Loeffler found that 1/30 gram of the contents of the vesicles +killed a calf of two hundred kilograms weight, and assuming that the +essential poison was present in the fluid in one part to five hundred +it would be several hundred times more powerful than the tetanus +poison. Further, the disease produced by inoculation of the filtrate +was itself inoculable and could be transmitted from animal to animal. +It was also found that when the virus was filtered several times it +ceased to be inoculable, showing that each time the fluid was passed +through the filter some of the minute organisms contained in it were +held back. + +It is not known whether these organisms belong to the bacteria or +protozoa, and naturally nothing is known as to their form, size and +structure. Up to the present about twenty diseases are known to be due +to a filterable virus, and among these are some of the most important +for animals and for man. Among the human diseases, yellow fever, +poliomyelitis, and dengue are so produced; of the animal diseases in +addition to foot and mouth disease, pleuropneumonia, cattle plague, +African horse sickness, several diseases of fowls and the mosaic +disease of the tobacco plant have all been shown to be due to a +filterable virus. Of these organisms the largest is that which +produces pleuropneumonia in cattle, and this alone has been +cultivated. It gives a slight opacity to the culture fluids, and when +magnified two thousand diameters appears as a minute spiral or round +or stellate organism having a variety of forms. Its size is such that +it passes the coarse, but is held back by the finer, filters and it is +possible that this does not belong to the same class with the +others.[1] The diseases produced by the filterable viruses taken as a +class show much similarity. They run an acute course, are severe, and +the immunity produced by the attack endures for a long time. + +Considered in its biological relations, infection is the adaptation of +an organism to the environment which the body of the host offers. It +is rather singular that variations in organisms represented by such +adaptation do not more frequently arise, in which case new diseases +would frequently occur. It cannot be denied that new diseases appear, +but there is no certain evidence that they do, and there is equally no +evidence that diseases disappear. From the meagre descriptions of +diseases, usually of the epidemic type, which have come down to us +from the past, it is difficult to recognize many of the diseases +described. The single diseases are recognized by comparing the causes, +the lesions and the symptoms with those of other diseases, and new +diseases are constantly being separated off from other diseases having +more or less common features. Many new diseases have been recognized +and named, but it is always more than probable that previously they +were confounded with other diseases. Smallpox is such a characteristic +disease that one would think it would have been recognized as an +entity from the beginning, but although the description of some of the +epidemics in remote times conform more or less to the disease as we +know it, the first accurate description is in the eighth century by +the Arabian physician Rhazes. Cerebro-spinal meningitis was not +recognized as a separate disease until 1803, diphtheria not until +1826, and the separation between typhoid and typhus fever was not made +before 1840. Nor is it sure that any diseases have disappeared, +although there seems to have been a change in the character of many. +It is difficult to reconcile leprosy as it appears now with the +universal horror felt towards it, due to the persistence of the old +traditions. It is possible, however, that the disease has not changed +its character, but that such diseases as smallpox, syphilis, and +certain forms of tuberculosis were formerly confounded with leprosy, +thus giving a false idea of its prevalence. + +In certain cases the adaptation of the organism is for a narrow +environment; for example, the parasitism may extend to a simple +species only, in others the adaptation may extend to a number of +genera. In certain cases the adaptation is mutual, extending to both +parasite and host and resulting in symbiosis, and this condition may +be advantageous for both. Certain of the protozoa harbor within them +cells of algae utilizing to their own advantage the green chlorophil of +the algae in obtaining energy from sunlight and in turn giving +sustenance to the algae. Although the algae are useful guests, when they +become too numerous the protozoan devours them. It is evident that +symbiosis is the most favorable condition for the existence of the +parasite, and an injurious action exerted by the parasite on the host +unfavorable. The death of the host is an unfortunate incident from the +parasite's point of view in that it is deprived of habitation and food +supply, being placed in the same unfortunate situation as may befall a +social parasite by the death of his host. + +FOOTNOTE: +[1] Flexner has recently succeeded in isolating and cultivating the +organism of poliomyelitis, but the organism is so small that its +classification is not possible. + + + + +CHAPTER VII + +THE NATURE OF INFECTION.--THE INVASION OF THE BODY FROM ITS +SURFACES.--THE PROTECTION OF THESE SURFACES.--CAN BACTERIA PASS +THROUGH AN UNINJURED SURFACE.--INFECTION FROM WOUNDS.--THE WOUNDS IN +MODERN WARFARE LESS PRONE TO INFECTION.--THE RELATION OF TETANUS TO +WOUNDS CAUSED BY THE TOY PISTOL.--THE PRIMARY FOCUS OR ATRIUM OF +INFECTION.--THE DISSEMINATION OF BACTERIA IN THE BODY.--THE DIFFERENT +DEGREES OF RESISTANCE TO BACTERIA SHOWN BY THE VARIOUS ORGANS.--MODE +OF ACTION OF BACTERIA.--TOXIN PRODUCTION.--THE RESISTANCE OF THE BODY +TO BACTERIA.--CONFLICT BETWEEN PARASITE AND HOST.--ON BOTH SIDES MEANS +OF OFFENSE AND DEFENSE.--PHAGOCYTOSIS.--THE DESTRUCTION OF BACTERIA BY +THE BLOOD.--THE TOXIC BACTERIAL DISEASES.--TOXIN AND +ANTITOXIN.--IMMUNITY.--THE THEORY OF EHRLICH. + + +As has been said, infection consists in the injury of the body by +living organisms which enter it. The body is in relation to the +external world by its surfaces only, and organisms must enter it by +some one of these surfaces. It is true that the bacteria in the +intestine--either those normally present or unusual varieties--may, +under certain circumstances, produce substances which are injurious +when absorbed; but this is not infection, and is analogous to any +other sort of poisoning. Each surface of the body has its own +bacterial flora. Organisms live on the surface either on matter which +is secreted by the surface or they use up an inappreciable amount of +body material. Many of these bacteria are harmless, some are +protective, producing by their growth such changes in the surface +fluids that these become hostile to the existence of other and +pathogenic forms. The surfaces also frequently harbor pathogenic +organisms which await some condition to arise which will permit them +to effect entrance into the tissues. + +The surfaces of the body protect from invasion to a greater or less +degree. The skin protects by the impervious horny layer on the +outside, the external cells of which are dead and constantly being +thrown off. Bacteria are always found on and in this layer, but the +conditions for growth here are not very favorable and the surface is +constantly cleansed by desquamation. The new cells to supply the loss +are produced in the deepest layer of the epidermis, and the movement +of cells and fluids takes place from within outwards. The protection +is less perfect about the hairs and the sweat glands. Infection by the +route of the sweat glands is, however, uncommon, for the sweat is a +fluid unfavorable for bacterial growth and the flow acts mechanically +in washing away organisms which may have entered the ducts. Infection +by the route of the hair follicles is common. There is no mechanical +cleansing as by the sweat, the space around the hair is large and the +accumulated secretion of the hair glands and the desquamated cells +furnish a material in which bacteria may grow. Growing as a mass in +this situation, they may produce sufficient toxic material to destroy +adjacent living cells and thus effect entrance. Infection from the eye +is not common, the surface, though moist, is smooth; the eyelashes +around the margin of the lids give some mechanical protection from the +entrance of bacteria contained in dust, and the movements of the lids +and the constant and easily accelerated secretion of tears act +mechanically in removing foreign substances. It is possible that the +mechanical cleansing of the skin by the daily bath may have some +action in preventing infection. + +The internal surfaces are much more exposed to attack and the +protection is not so efficient. The moisture of these surfaces is both +a protection and a source of danger. It protects by favoring the +lodgment near the orifices of organisms which are in the inspired air, +for when bacteria touch a moist surface they cannot be raised from +this and carried further by air currents. The moisture is a source of +danger in that it favors the growth of bacteria which lodge on the +surface. The respiratory surface which is most exposed to infection +from the air is further protected by the cilia, which are fine +hair-like processes covering the cells of the surface and which by +their constant motion sweep out fine particles of all sorts which +lodge upon them. The cavity of the mouth harbors large numbers of +organisms, many of them pathogenic. It forms a depot from which +bacteria may pass to communicating surfaces and infection from these +may result. Food particles collect in the mouth and provide culture +material, and there are many crypts and irregularities of surface +which oppose mechanical cleaning. Infection of the middle ear, the +most common cause of deafness, takes place by means of the Eustachian +tube which connects the cavity of the ear with the mouth. Organisms +from the mouth can extend into the various large salivary glands by +means of the ducts and give rise to infections. The tonsils, +particularly in children, provide a favorable surface for infection. +The mucous surface extends into these forming deep pockets lined with +very thin epithelium, and in these debris of all sorts accumulates and +provides material favorable for bacterial growth. + +The lungs at first sight seem to offer the most favorable surface for +infection. The surface, ninety-seven square yards, is enormous; it is +moist, the epithelial covering is so thin as to give practically no +mechanical protection, large amounts of air constantly pass in and +out, and the surface is in contact with this. They are protected from +infection in many ways. The tubes or bronchi by which the air passes +into and from the lungs are covered with cilia; the surface area of +these tubes constantly enlarges as they branch, the sum of the +diameters of the small tubes being many times greater than that of the +windpipe, and this enlargement by retarding the motion of the air +favors the lodgment of particles on the surface whence they are +removed by the action of the cilia. The entering air is also brought +closely in contact with a moist surface at the narrow opening of the +larynx. That bacteria and other foreign substances can enter the lungs +in spite of these guards is shown not only by the infections which +take place here, but also by the large amount of black carbon +deposited in them from the soot contained in the air. + +Infection rarely takes place from the surface of the gullet or +oesophagus which leads from the mouth to the stomach. This is due to +the smoothness of the surface and to the rapidity with which food +passes over it. Infection by the stomach also is rare, for this +contains a strong acid secretion which destroys many of the bacteria +which are taken in with the food. It is found impossible to infect +animals with cholera unless the acidity of the stomach contents be +neutralized by an alkali. Many organisms, although their growth in the +stomach is inhibited, are not destroyed there and pass into the +intestines, where the conditions for infection are more favorable. +This large and very irregular surface is bathed in fluid which is a +good culture medium and but a single layer of cells covers it. The +organisms which cause many of the infectious diseases in both man and +animals find entrance by means of the alimentary canal, as cholera, +dysentery, typhoid fever, chicken cholera, hog cholera. + +Infection by the genito-urinary surface is comparatively rare. The +surface openings are usually closed, and the discharge of urine has a +mechanical cleansing effect. The wide tube of the vagina is further +protected by a normal bacterial flora which produces conditions +hostile to other and pathogenic bacteria. The most common infections +are the sexual diseases, which are due to organisms which find +favorable conditions for growth in and on the surface and which are +conveyed from a similar surface by sexual contact. + +It remains a question whether bacteria can penetrate an intact surface +producing no injury at the point of entrance and be carried by the +lymph or blood into internal organs where they produce disease. +Internal infections are often found with seemingly intact body +surfaces, but it is impossible to exclude the presence of minute or +microscopic surface injuries by which the organisms may have entered. +It is also possible that a slight injury at the point of entrance may +heal so completely as to leave no trace. + +The chief danger from wounds is that their surfaces may become +infected. Death from wounds is due more frequently to infection than +to the actual injury represented by the wounds. Much depends upon the +character of the wound. Infection of clean wounds which are made by a +sharp cutting instrument and from which there is abundant haemorrhage +with sealing of the edges of the wound by clotted blood, rarely +happens. Typical wounds of this sort are often made in shaving, and +infection of such wounds is extraordinarily rare. If, with the wound, +pathogenic organisms are placed in the tissue, or foreign substances +such as bits of clothing are carried in with a bullet, for example, or +if the instrument causing the wound be of such a character as to +produce extensive lacerations of tissue, infection is more apt to +occur. The less frequency of infection in modern wars is in part due +to the simpler character of the wounds and in part to the fact that +modern fixed ammunition is practically free from germs. The old +spear-head, the arrow, the cross bow bolt, had little regard for the +probabilities of infection. Whether infection follows a wound depends +both upon the entry of pathogenic organisms and upon these finding in +the tissues suitable opportunities for growth. In wounds in which +there is much laceration of tissue organisms find the most favorable +conditions for development. The very slight wounds produced by the +exploded cap in the toy pistol give suitable conditions for the +development of the bacillus which produces tetanus or lockjaw. The +deaths of children from lockjaw following a Fourth of July celebration +have often exceeded the total deaths in a Central American revolution. +The tetanus bacillus is a widely distributed organism, whose normal +habitat is in the soil and which is usually present on the dirty hands +of little boys. The toy-pistol wounds are made by small bits of paper +or metal being driven into the skin by the explosion of the cap. The +wound is of little moment, the surface becomes closed, and a bit of +foreign substance, a few dead cells and the tetanus bacilli from the +surface remain enclosed and in a few days the fatal disease develops. +Infection of the surfaces of old wounds such as the surface of an +ulcer takes place with difficulty. Large numbers of leucocytes which +give protection by phagocytosis are constantly passing to the surface, +and there is also a constant stream of fluid towards the surface. On +such a surface there may be an abundant growth of pathogenic +organisms, but no infection results. + +In most infections there is a focus where the infectious organisms are +localized; this may correspond to the point of entrance on a surface +or it may be in the interior of the body, the organisms being +deposited there after entrance. At this primary localization, the +_atrium_ of infection,[1] the organisms multiply and from this +point further invasion takes place. Many secondary foci may be formed +in the organs by distribution of the organisms, or there may be +infection of the blood and fluids of the body. The injuries which are +produced depend upon the nature of the infecting organisms. The most +common lesion consists in the death of the tissue about the infecting +organisms. In most cases the sum of the changes are so characteristic +that from them the nature of the infection is easily determined, and +these changes often give names to the disease; thus tuberculosis is a +disease characterized by the formation of tubercles or little nodules +in the body. The situation of the foci of disease is determined by +many conditions, the most important being the varying resistance of +the different organs of the body to the growth of bacteria. Certain +organs, such as the central nervous system, the muscles, the testicles +and the ovaries, have a high resistance to the growth of bacteria. The +disease may be localized in certain organs because only in these do +the bacteria find favorable conditions for growth. In spite of a high +general resistance to infection the lesions in chronic glanders are +most marked in the muscles, those of poliomyelitis in the spinal cord. +There are few bacterial diseases which are localized in the blood, but +many of the diseases caused by protozoa have this localization. In +every infection some organisms enter the blood, which acts as a +carrier and deposits them in the organs. + +Bacteria cause disease by producing substances called toxines which +are poisonous to the cells, and of which two sorts are distinguished. +One form of toxines is produced by the bacteria as a sort of +secretion, and is formed both in the body and when the bacteria are +growing in cultures. Substances of this character, many of them highly +poisonous, are produced both by animals and plants. They may serve the +purpose both of offence and defence, as in the case of the snake +venom, and in other cases they seem to benefit their producers in no +way whatever, and may even be injurious to them. After the different +cereals have been grown for succeeding years in the same place, growth +finally diminishes not from the exhaustion of the soil, but from the +accumulation in it of substances produced by the plants. Beneath +certain trees, as the Norway maple, grass will not grow, and it has +been shown that the tree produces substances which inhibit the growth +of grass. When bacteria are grown in a culture flask, growth ceases +long before the nutritive material has been consumed, from the +accumulation of waste products in the fluid. The other class of toxic +substances, called endotoxines, are not secretion products, but are +contained in the bacterial substance and become active by the +destruction and disintegration of the bacteria. They can be +artificially produced by grinding up masses of bacteria, and in the +body the destruction and solution of bacteria which is constantly +taking place sets them free. The toxines and the endotoxines are of an +albuminous nature, and act only when they come in contact with the +living cells within the body. When taken into the alimentary canal +they are either not absorbed or so changed by the digestive fluids as +to be innocuous. Many of the ordinary food substances, even a material +apparently so simple as the white of an egg, are highly injurious if +they reach the tissues in an unchanged form. + +By means of these substances the bacteria produce such changes in +their environment within the body that this becomes adapted to their +parasitic existence. In symbiosis the bacteria probably undergo +changes by which they become adapted to the environment, and in +parasitism the environment becomes adapted to them. In the same way +man can change his immediate environment by means of clothing, +artificial heating, etc., and adapt it to his needs; or by hardening +his body he can adapt it to the environment. The pathogenic bacterium +finds the living tissue hostile, its cells devour him, the tissue +fluids destroy him, and by means of the toxines he changes the +environment from that of living to dead tissue, or in other ways so +alters it that it is no longer hostile. The parasite has also means of +passive defence comparable to the armor of the warrior in the past. It +may form a protective mantle called a capsule around itself, which +serves to protect it from the action of the body fluids. Such capsule +formation is a very common thing in the pathogenic organisms, and they +are found only when these are growing in the body and do not appear in +cultures (Fig. 17-c). + +It is evident that just as the parasite has his weapons of offence and +defence so has the host, otherwise there would be no recovery from +infectious diseases. Although many of the infectious diseases have a +high mortality, which in rare instances reaches one hundred per cent, +the majority do recover. In certain cases the recovery is attended by +immunity, the individual being protected to a greater or less degree +from a recurrence of the same disease. The immunity is never absolute; +it may last for a number of years only, and usually, if the disease be +again acquired, the second attack is milder than the primary. Probably +the most enduring immunity is in smallpox, although cases are known of +two and even three attacks; the immunity is high in scarlet fever, +measles, mumps and typhoid fever. The immunity from diphtheria is +short, and in pneumonia, although there must be a temporary immunity, +future susceptibility to the disease is probably increased. In certain +cases the immunity is only local; the focus of disease heals because +the tissue there has evolved means of protection from the parasite, +but if any other part of the body be infected, the disease pursues the +usual course. A boil, for example, is frequently followed by the +appearance of similar boils in the vicinity due to the infection of +the skin by the micrococci from the first boil, which by dressings, +etc., have become spread over the surface. + +The natural methods of defence of the host against the parasites have +formed the main subject in the study of the infectious diseases for +the last twenty years. Speculation in this territory has been rife and +most of it fruitless, but by patient study of disease in man and by +animal experimentation there has been gradually evolved a sum of +knowledge which has been applied in many cases to the treatment of +infectious diseases with immense benefit. Research was naturally +turned to this subject, for it was evident that the processes by which +the protection of the body was brought about must be known before +there could be a really rational method of treatment directed towards +the artificial induction of such processes, or hastening and +strengthening those which were taking place. Previous to knowledge of +the bacteria, their mode of life, their methods of infection and +knowledge of the defences of the body, most of the methods of +prevention and treatment of the infectious diseases was based largely +on conjecture, the one brilliant exception being the discovery of +vaccination by Jenner in 1798. + +The host possesses the passive defences of the surfaces which have +already been considered. The first theories advanced in explanation of +immunity were influenced by what was known of fermentation. One, the +exhaustion theory, assumed that in the course of disease substances +contained in the body and necessary for the growth of the bacteria +became exhausted and the bacteria died in consequence. Another, the +theory of addition, assumed that in the course of the disease +substances inimical to the bacteria were formed. Both these theories +were inadequate and not in accord with what was known of the +physiology of the body. The most general mode of defence is by +phagocytosis, the property which many cells have of devouring and +digesting solid substances (Fig. 16-p). Although this had been known +to take place in the amoebae and other unicellular organisms, the wide +extent of the process and its importance in immunity was first +recognized by Metschnikoff in 1884 and the phagocytic theory of +immunity advanced and defended by a brilliant series of experiments by +Metschnikoff and his pupils conducted in the Pasteur Institute. +Metschnikoff's first observations were made on the daphnea, a small +animalcule just visible to the naked eye which lives in fresh water. +The structure of the organism is simple, consisting of an external and +internal surface between which there is a space, the body cavity; +daphneae are transparent and can be studied under the microscope while +living. Metschnikoff observed that certain of them in the aquarium +gradually lost their transparency and died, and examining these he +found they were attacked by a species of fungus having long, thin +spores. These spores were taken into the intestine with other food; +they penetrated the thin wall of the intestine, passed into the body +cavity, multiplied there, and in consequence the animal died. In many +cases, however, those penetrating became enclosed in cells which the +body cavity contains and which correspond with the leucocytes of the +blood; in these the spores were digested and destroyed. The daphneae in +which this took place recovered from the infection. Here was a case in +which all the stages of an infectious disease could be directly +followed under the microscope, and the whole process was simple in +comparison with infections in the higher animals. The pathogenic +organism was known, the manner and site of invasion was clear, it was +also evident that if the multiplication of the parasite was unchecked +the animal died, but if the parasite was opposed by the body cells and +destroyed the animal recovered. The studies were carried further into +the diseases of the higher animals, and it was found the leucocytes in +these played the same part as did the cells in the body cavity of the +daphnea. The introduction of bacteria into certain animals was +followed by their destruction within cells and no disease resulted; if +this did not take place, the bacteria multiplied and produced disease. +Support also was given the theory by the demonstration at about the +same time that in most of the infectious diseases the leucocytes of +the blood became increased in number,--that in pneumonia, for +instance, instead of the usual number of eight thousand in a cubic +millimeter of blood, there were often thirty thousand or even fifty +thousand. At about the same time also chemotaxis, or the action of +chemical substances in attracting or repelling organisms, excited +attention, and all these facts together became woven into the theory. +It was soon seen, however, that this theory, based as it was on +observation and supported by the facts observed, was not, at least in +its first crude form, capable of general application. Many animals +have natural immunity to certain diseases; they do not have the +disease under natural conditions, nor do they acquire the disease when +the organisms causing it are artificially introduced into their +tissues by inoculation. Such natural immunity seemed to be unconnected +with defence by phagocytosis, for the leucocytes of the animal might +or might not have phagocytic reaction to the particular organisms to +which the animal was immune. It was also seen that recovery from +infection in certain diseases was unconnected with phagocytosis. It +had also been demonstrated, by German observers chiefly, that the +serum of the blood, the colorless fluid in which the corpuscles float, +was itself destructive, and that in an animal rendered immune to a +special bacterium the destructive action of the serum on that organism +was greatly increased. In this hostile serum the bacteria often became +clumped together in masses, the bodies became swollen, broken up, and +finally disintegrated. This property of the serum was described as due +to a substance in the serum called _alexine_, which in the immune +animal became greatly increased in amount. It was even denied by some +that phagocytosis of living bacteria took place, and that all those +included in the cells were dead, having been destroyed in the first +instance by the serum. The strife became a national one between the +French and Germans,--on the one side in France the phagocytic theory +was defended, and in Germany, on the other, the theory of serum +immunity. The mass of experimental work which poured from the +laboratories of the two countries in attack and defence became so +great that it could not easily be followed. It had a good influence +because, without the stimulation of this national rivalry, the +knowledge which gradually arose from this work would not have been so +quickly acquired. It is interesting that the mode of action of the +serum in destroying bacteria was demonstrated not by a German but by +Bordet, a French observer and a pupil of Metschnikoff. He showed that +the serum contained two distinct substances, each necessary for the +destructive action. The separate action of these substances can be +studied since one is _thermolabile_, or destroyed by heating the +serum to one hundred and thirty-three degrees; the other +_thermostabile_, or capable of withstanding a greater degree of +heat. These substances are known only by their effect, they have never +been separated from the serum. The thermostabile substance, or +_amboceptor_, as it is generally called, has in itself no +destructive action on the bacteria; but in some way so alters them +that they can be acted on by the thermolabile substance called +_complement_ whose action is destructive. The amount of +amboceptor may increase in the course of infection and its formation +stimulated, the amount of complement remains unchanged. The action of +the amboceptor is specific, that is, directed against a single species +of bacterium only; the destructive power of the blood may be very +great against a single bacterium species and have no effect on others. +There seem naturally to be many different amboceptors in the blood, +and the number may be very greatly increased. It has been shown as a +result of the work of many investigators that the shield has two +faces,--there is destruction both by cells and fluids and there is +interaction by both. The amboceptors so necessary for the destructive +action of the serum are produced by the body cells, particularly the +leucocytes. The serum assists in pagocytosis by the action on bacteria +of substances called _opsonins_ which are contained in it, and +the formation of which can be very greatly stimulated. Again, not all +inclusion of bacteria within leucocytes is indicative of phagocytosis; +in many cases the bacteria seem to find the best conditions for +existence within the leucocytes, and these and not the bacteria are +destroyed. + +So far it has been shown that the best defence of the body is, as is +the best defence in war, by offensive measures, as illustrated by +phagocytosis and destruction by the serum. Both of these actions can +be increased by their exercise just as the strength of muscular +contraction can be increased by exercise, and the facility for doing +everything increased by habit. Certain of the infectious diseases are, +as has been said, essentially toxic in their nature, and in cultures +the organisms produce poisonous substances. By the injection into the +tissues of such substances the same disturbances are produced as when +the bacteria are injected. Such a disease is diphtheria. In this there +is only a superficial invasion of the tissues. The diphtheria bacilli +are located on the surface of the tonsils or pharynx or windpipe, +where, as a result of their action, the membrane so characteristic of +the disease is produced. The membrane may be the cause of death when +it is so extensively formed as to occlude the air passages, but the +prominent symptoms of the disease, the fever, the weakness of the +heart and the great prostration are due not to the presence of the +membrane, but to the action of toxic substances which are formed by +the bacteria growing in the superficial lesions and absorbed. Tetanus, +or lockjaw, is another example of these essentially toxic diseases. +The body must find some means of counteracting or destroying these +injurious toxic substances. It does this by forming antagonistic +substances called antitoxines, which act not by destroying the +toxines, but by uniting with them, the compound substance being +harmless. It has been found that the production of antitoxine can be +so stimulated by the injection of toxine that the blood of the animal +used for the purpose contains large amounts of antitoxine. The horse +is used in this way to manufacture antitoxine, and the serum injected +into a patient with diphtheria has a curative action, a greater amount +being thus introduced than the patient can manufacture. + +[Illustration: FIG. 18.--DIAGRAM TO ILLUSTRATE EHRLICH'S THEORY OF +ANTITOXINE FORMATION. The surface of the cell (_n_) is covered with +receptors some of which (_b_) fit the toxine molecule, (_a_) allowing +the toxine to act upon the cell. Under the stimulus of this the cell +produces these receptors in excess which enter into the blood and +there combine with the toxine as in _a^1 b^1_, thus anchoring it and +preventing it from acting upon the cells. The receptors _c_ and _d_ do +not fit the toxine molecule.] + +A very ingenious theory which well accords with the facts has been +given by Ehrlich in explanation of the production of antitoxine and of +the reaction between toxine and antitoxine (Fig. 18). This is based on +the hypothesis, which is in accord with all facts and generally +accepted, that the molecules which enter into the structure of any +chemical substance have in each particular substance a definite +arrangement, and that in a compound substance each elementary +substance entering into the compound molecule has chemical affinities, +most of which may be satisfied by finding a suitable mate. Ehrlich +assumes that the very complex chemical substances which form the +living cells have many unsatisfied chemical affinities, and that it is +due to this that molecules of substances adapted for food can enter +the cells and unite with them; but there must be some coincidence of +molecular structure to enable the union to take place, the comparison +being made of the fitting of a key into a lock. The toxines--that +produced by the diphtheria bacillus being the best example--are +substances whose molecular structure enables them to combine with the +cells of the body, the combination being effected through certain +chemical affinities belonging to the cells termed _receptors_. +Unless the living cells have receptors which will enable the +combination with the toxine to take place, no effect can be produced +by the toxine and the cells are not injured. This is the case in an +animal naturally immune to the action of the diphtheria bacillus or +its toxines. In the case of the susceptible animal the receptors of +the cells of the different organs combine with the toxine to a greater +or less extent, which explains the fact that different degrees of +injury are produced in the different tissues; the toxine of tetanus, +or lockjaw, for example, combines by preference with the nervous +tissue, that of diphtheria with the lymphatic tissue. It is known that +in accordance with the general law of injury and repair, a loss in any +part of the body stimulates the tissue of the same kind to new growth +and the loss is thus repaired; it is assumed that the cell receptors +which combine with the toxine are lost for the cell which then +produces them in excess. The receptors so produced pass into the +blood, where they combine with the toxine which has been absorbed; the +combination is a stable one, and the toxine is thus prevented from +combining with the tissue cells. The antitoxine which is formed during +the disease, and the production of which in the horse can be +enormously stimulated by the injection of toxine, represents merely +the excess of cell receptors, and when the serum of the horse +containing them is injected in a case of diphtheria the same +combination takes place as in the case of receptors provided by the +patient. In the case of the destruction of bacteria in the blood by +the action of amboceptor and complement, the amboceptor must be able +to combine with both the bacterial cell and the complement which +brings about its destruction, and just as antitoxine is formed so new +amboceptors may be formed. + +Few hypotheses have been advanced in science which are more ingenious, +in better accord with the facts, have had greater importance in +enabling the student to grasp the intricacies of an obscure problem, +and which have had an equal influence in stimulating research. The +immunity which results from disease in accordance with this theory, is +due not to conditions preventing the entrance of organisms into the +body, but to greater aptitude on the part of the cells to produce +these protective substances having once learned to do so. An +individual need not practise for many years, having once learned them, +those combinations of muscular action used in swimming; but the habit +at once returns when he falls into the water. + +Infectious diseases and recovery are phases of the struggle for +existence between parasite and host, and illustrate the power of +adaptation to environment which is so striking a characteristic of +living matter. + +FOOTNOTES: + +[1] The comparison here is with the atrium of a Pompeiian house. + + + + +CHAPTER VIII + +SECONDARY, TERMINAL AND MIXED INFECTIONS.--THE EXTENSION OF INFECTION +IN THE INDIVIDUAL.--TUBERCULOSIS.--THE TUBERCLE BACILLUS.--FREQUENCY +OF THE DISEASE.--THE PRIMARY FOCI.--THE EXTENSION OF BACILLI.--THE +DISCHARGE OF BACILLI FROM THE BODY.--INFLUENCE OF THE SEAT OF DISEASE +ON THE DISCHARGE OF BACILLI.--THE INTESTINAL DISEASES.--MODES OF +INFECTION.--INFECTION BY SPUTUM SPRAY.--INFECTION OF WATER +SUPPLIES.--EXTENSION OF INFECTION BY INSECTS.--TRYPANOSOME +DISEASES.--SLEEPING SICKNESS.--MALARIA.--THE PART PLAYED BY +MOSQUITOES.--PARASITISM IN THE MOSQUITO.--INFECTION AS INFLUENCED BY +HABITS AND CUSTOMS.--HOOKWORM DISEASE.--INTER-RELATION BETWEEN HUMAN +AND ANIMAL DISEASES.--PLAGUE.--PART PLAYED BY RATS IN +TRANSMISSION.--THE PRESENT EPIDEMIC OF PLAGUE. + + +The infectious diseases are often complicated by secondary infections, +some other organism finding opportunity for invasion in the presence +of the injuries produced in the primary disease. In many diseases, +such as diphtheria, scarlet fever and smallpox, death is frequently +due to the secondary infection. The secondary invaders not only find +local conditions favoring a successful attack, but the activity of the +tissue cells on which the production of protective substances +essentially depends has suffered by the primary infection, or the +cells are occupied in meeting the exigencies of this. The body is in +the position of a state invaded by a second power where all its forces +and resources are engaged in repelling the first attack. + +What are known as terminal infections occur shortly before death. No +matter what the disease which causes death, in the last hours of life +the body usually becomes invaded by organisms which find their +opportunity in the then defenceless tissues, and the end is often +hastened by this invasion. + +There are also mixed infections in which two different organisms unite +in attack, each in some way assisting in the action of the other. The +best known example of this is in the highly infectious disease of +swine known as hog cholera. It has been shown that in this disease two +organisms are associated,--one an invisible and filterable organism, +and the other a bacillus. It was first supposed that the bacillus was +the specific organism; it was found in the lesions and certain, but +not all, the features of the disease were produced by inoculating hogs +with pure cultures. The disease so produced is not contagious, and the +contagious element seems to be due to the filterable virus. + +The modes of transmission of infectious diseases are of great +importance and are the foundation of measures of public health. In the +preceding chapter we have seen that in the infected individual the +disease extends from one part of the body to another. There is a +primary focus of disease from which the extension takes place, and the +study of the modes of extension in the individual throws some light on +the much more difficult subject of the transmission of disease from +one individual to another. There are four ways by which extension in +the individual may take place. + +1. By continuity of tissue, an adjoining tissue or organ becoming +infected by the extension of a focus of infection. + +2. By means of lymphatics. Organisms easily enter these vessels which +are in continuity with the tissue spaces and receive the exudate from +the focus of infection. The organisms are carried to the lymph nodes, +which, acting as filters, retain them and for a time prevent a further +extension. The following illustrates the importance of the part the +nodes may play in mechanically holding back a flood of infection. A +physician examined after death the body of a person who died from +infection with a very virulent micrococcus and in the course of the +examination slightly scratched a finger. One of the organs of the body +was removed, sent to a laboratory and received by a laboratory worker, +a woman physician, who had slight abrasions and fissures in the skin +of the hands from contact with irritating chemicals. In the course of +a few hours the wound on the finger of the man became inflamed, +intensely painful, and red lines extended up the arm in the course of +the lymphatic vessels, showing that the organisms were in the +lymphatics and causing inflammation in their course. The lymph nodes +in the armpit into which these vessels empty became greatly inflamed, +swollen, and an abscess formed in them which was opened. There was +high fever, great prostration, a serious illness from which the man +did not recover for several months. The woman only handled the organ +which was sent to the laboratory in order to place it in a fluid for +preservation. She also had a focus of infection of a finger with the +same red lines on the arm, showing extension by the lymphatics; but +there was no halt of the infection in the armpit, for all the lymph +nodes there had been removed several years before in the course of an +operation for a tumor of the breast. A general infection of the blood +took place, there was very high fever, and death followed in a few +days. The halt of the infection is important in allowing time for the +body to make ready its means of defence. One cannot avoid comparing +the lymph node with a strong fortress thrown in the path of a +victorious invading army behind which the defenders may gather and +which affords them time to renovate their strength. + +3. By means of the blood. The blood vessels are universally +distributed, the smaller vessels have thin walls easily ruptured and +easily penetrated. It is probable that in every infection some +organisms enter the blood which, under usual conditions, is peculiarly +hostile to bacteria. These may, however, be carried by the blood to +other organs and start foci of infection in these. + +4. By means of continuous surfaces. The bacteria may either grow along +such surfaces forming a continuous or more or less broken layer, or +may be carried from place to place in the fluids which bathe them. + +All these modes of extension are well shown in tuberculosis. This +disease is caused by a small bacillus which does not produce spores, +has no power of saphrophytic growth under natural conditions, and is +easily destroyed. Moisture and darkness are favorable conditions for +its existence, sunlight and dryness the reverse. There are three +varieties or strains of the tubercle bacilli which infect respectively +man, cattle and birds, and each class of animals shows considerable +resistance to the varieties of the bacillus which are most infectious +for the others. + +The primary seat of the infection in man is generally in the upper +part of the lung. The organisms settle on the surface here and cause +multiplication of the cells and an inflammatory exudate in a small +area. With the continuous growth of the bacilli in the focus, +adjoining areas of the lung become affected, and there is further +extension in the immediate vicinity by means of the lymphatics. Small +nodules are formed and larger areas by their coalescence. Infection +with tuberculosis is so common that at least three-fourths of all +individuals over forty show evidences of it. The examination of two +hundred and twenty-five children of the average age of five years who +had died of diphtheria showed tuberculous infection in one-fifth of +the cases and the frequency of infection increases with age. The +defence on the part of the body is chiefly by the formation of dense +masses of cicatricial tissue which walls off the affected area and in +which the bacilli do not find favorable conditions for growth. This +mode of defence, which is probably combined with the production of +substances antagonistic to the toxines produced by the bacilli, is so +efficacious that in the great majority of cases no further extension +of the process takes place. In certain cases, however, the growth of +the bacilli in the focus is unchecked, the tissue about them is killed +and becomes converted into a soft semi-fluid material; further +extension then takes place. All parts of the enormous surface of the +lungs are connected by means of the system of air tubes or bronchi, +and the bacilli have favorable opportunity for distribution, which is +facilitated by sudden movements of the air currents in the lung +produced by coughing. The defence of the body can still keep pace with +the attack, and even in an advanced stage the infection can be checked +in some cases permanently; in others the check is but temporary, the +process of softening continues, and large cavities are produced by the +destruction of the tissue. On the inner surface of these cavities +there may be a rapid growth of bacilli. + +From the lungs the bacilli are carried by the lymphatics to the lymph +nodes at the root of the lungs, in which a similar process takes +place; this, on the whole, is favorable, because further extension by +this route is for a time blocked. The extension by means of surfaces +continues, the abundant sputum which is formed in the lungs and which +contains large numbers of bacilli, becomes the vehicle of +transportation. The windpipe and larynx may become infected, the back +parts of each are more closely in contact with the sputum and are the +parts most generally infected. A large part of the sputum is swallowed +and infection of the intestine takes place, the lesions taking the +form of large ulcers. From the intestinal ulcers there is further +extension by means of the lymphatics, to the large lymph nodes in the +back of the abdominal cavity (Fig. 8-25); the bacilli may also pass +from the ulcers into the abdominal cavity and be distributed over the +surface of the peritoneum resulting in tuberculous peritonitis. When +the disease has reached an advanced stage, bacilli in small numbers +continually pass into the blood and are distributed by this over the +body, producing small nodules in many places. In rare cases +distribution by the blood is the principal method of extension, and +immense numbers of small foci of disease are produced, the form of +disease being known as acute miliary tuberculosis. Although the +bacilli are distributed everywhere, certain organs, as the brain and +muscles, are usually exempt, because in these the conditions are not +favorable to further growth of the bacilli. Tuberculosis, although +frequently a very acute disease, is usually one of the best types of a +chronic disease and may last for many years. The chronic form is +characterized by periods of slow or rapid advance when conditions +arise in the body favorable for the growth of the bacilli, and periods +when the disease is checked and quiescent, the defensive forces of the +body having gained the upper hand. Often the intervention of some +other disease so weakens the defences of the body that the bacilli +again find their opportunity. Thus typhoid fever, scarlet fever and +other diseases may be followed by a rapidly fatal advance of the +tuberculosis, starting from some old and quiescent focus of the +disease. + +Tuberculosis is also one of the best examples of what is known as +latent infection. In this the infectious organisms enter the body and +produce primary lesions in which the organisms persist but do not +extend owing to their being enclosed in a dense and resistant tissue, +or to the production of a local immunity to their action. Dr. Head has +recently examined the children of households in which there was open +tuberculosis in some member of the household. By open tuberculosis is +understood a case from which bacilli are being discharged. He found +with scarcely an exception that all the children in such families +showed evidences of infection. The detection of slight degrees of +tuberculous infection is now made easy by certain skin reactions on +inoculation of the skin with a substance derived from the tubercle +bacilli. Such latent infections may never become active and in the +majority of cases do not. When, however, in consequence of some +intercurrent disease or conditions of malnutrition the general +defences of the body become weakened extension follows. Such latent +infections explain the enormous frequency of tuberculosis in prisons. +Under the general prison conditions infection in the prisons probably +does not take place to any extent, and the disease is as common when +the prisoners are kept in individual cells as in common prisons. It is +probable that in these cases the prisoners have latent tuberculosis +when entering, and the disease becomes active under the moral and +physical depression which prison life entails. + +For the extension of infection from one individual to another the +infecting organisms must in some way be transferred. The most +important of the conditions influencing this are the localization of +the disease and the character of the infectious organisms, +particularly with regard to their resistance to the conditions met +with outside of the body. The seat of disease influences the discharge +of organisms; thus, if the disease involve any of the surfaces the +organisms become mingled with the secretions of the surface and are +discharged with these. If the seat of disease be in the lungs, the +throat or the mouth, the sputum forms the medium of extension, which +can take place in many ways. The sputum may become dried, forms part +of the dust and the organisms enter with the inspired air. The +organisms which cause most of the diseases in which the sputum becomes +infectious are quickly destroyed by conditions in the open, such as +the sunlight and drying; street dust does not play so prominent a part +in extension as is generally supposed. Organisms find much more +favorable conditions within houses. It is now generally recognized +that infection with tuberculosis does not take place in the open, but +in houses in which the bacilli on being discharged are not destroyed. +The hands, the clothing and surroundings even with the exercise of the +greatest care may become soiled with the saliva. + +It has been shown that in coughing and speaking very fine particles of +spray are formed by the intermingling of air and saliva, which may be +projected a considerable distance and remain floating in the air for +some time. These particles are so fine as to be invisible; they may be +inspired, and their presence in the air forms an area of indeterminate +extent around the infected person within which such infection is +possible. Such spray formation is also an important means of the +extension of infection in the sick individual, for it is continually +formed and inspired. It is in this way that the extreme prevalence of +broncho-pneumonia in infants and young children is to be explained. No +matter what the essential disease, an almost constant finding in young +children after death is small areas of inflammation in the lungs in +and around the terminations of the air tubes. The situation renders it +evident that the organisms which caused the lesions entered the lung +by the air tubes. The mouth of the child is unclean and harbors +numbers of the same sort of organisms as those causing the lung +inflammation; but in the absence of such a mode of infection as is +given by spray formation it is difficult to see how the extension from +the mouth to the lungs could take place. The weakened condition of the +body in these cases favors the secondary infection. + +If the disease be located in the intestines, as in typhoid fever and +dysentery, the organisms are contained in the fecal discharges, and by +means of these the infection is extended. In typhoid fever, dysentery +and cholera massive infections of the populace may take place from the +contamination of a water supply and the disease be extended over an +entire city. One of the most striking instances of this mode of +extension was in the epidemic of cholera in Hamburg in 1892. There +were two sources of water supply, one of which was infected, and the +cases were distributed in the city in the track of the infected +supply. Many such instances have been seen in typhoid fever. Certain +articles of food, particularly milk, serve as sources of infection. +This is more apt to happen when the organism causing the infection +grows easily outside of the body. A few such organisms entering into +the milk can multiply enormously in a few hours and increase the +amount of infectious material. In all these cases the sick individual +remains a source of infection, for it is almost impossible to avoid +some contamination of the body and the immediate surroundings with the +organisms contained in the discharges. + +Transmission by air plays but little part in the extension of +infection. In such a disease as smallpox, where the localization is on +the surface of the body, the organisms are contained in or on the thin +epithelial scales which are constantly given off. These are light, and +may remain floating in the air and carried by air currents just as is +the pollen of plants. There seem to have been cases of smallpox where +other modes of more direct transmission could be excluded and in which +the organisms were carried in the air over a considerable space. All +sorts of intermediate objects, both living and inanimate, such as +persons, domestic animals, toys, books, money, etc., can serve as +conveyors of infection. + +Insects play a most important part in the transmission of disease, and +in certain cases, as when a disease is localized in the blood, this is +the only means of transmission. There are three ways in which the +insect plays the role of conveyor. + +1. The insect may play a purely passive part in that its exterior +surface becomes contaminated with the discharges of the sick person, +and in this way the organisms of disease may be conveyed to articles +of food, etc. The ordinary house fly conveys in this way the organisms +of typhoid and dysentery. Flies seek the discharges not only for food, +but for the purpose of depositing their eggs, and the hairy and +irregular surface of their feet facilitates contamination and +conveyance. When flies eat such discharges the organisms may pass +through the alimentary canal unchanged and be deposited with their +feces; they also often vomit or regurgitate food, and in this way also +contaminate objects. Flies very greedily devour the sputum of +tuberculous patients, and the tubercle bacilli contained in this pass +through them unchanged and are deposited in their feces. + +[Illustration: FIG. 19.--TRYPANOSOMES FROM BIRDS. All the trypanosomes +are very much alike. They contain a nucleus represented by the dark +area in the centre and a fur-like membrane terminating in a long +whip-like flagellum. They have the power of very active motion within +the blood.] + +2. Diseases which are localized in the blood are transmitted by biting +flies. The biting apparatus becomes contaminated with the organisms +contained in the blood, and these are directly inoculated into the +blood of the next victim. The trypanosome diseases form the best +example of this mode of transmission. The trypanosomes are widely +distributed, exclusively parasitic, flagellated protozoa which live in +the blood of a large number of animals and birds (Fig. 19). They may +give rise to fatal diseases, but in most cases there is mutual +adaptation of host and parasite and they seem to do no harm. One of +the most dangerous diseases in man, the African sleeping sickness, is +caused by a trypanosome, and the disease of domestic cattle in Africa, +nagana, or tsetse fly disease, is also so produced. In certain regions +of Africa where a biting fly, the _Glossina morsitans_, occurs in +large numbers, it has long been known that cattle bitten by these +flies sickened and died, and this prevented the settling and use of +the land. In the blood of the sick cattle swarms of trypanosomes are +found. The source from which the tsetse fly obtained the trypanosomes +which it conveyed to the cattle was unknown until it was discovered +that similar trypanosomes exist in the blood of the wild animals which +inhabit the region, but these have acquired by long residence in the +region immunity or adaptation to the parasite and no disease is +produced. With the gradual extension of settlement of the country and +the accompanying destruction of wild life the disease is diminishing. +Some of the inter-relations of infections are interesting. The +destruction of wild animals in South Africa which, by removing the +sources of nagana, rendered the settlement of the country possible was +due chiefly to the introduction of another infectious disease, +rinderpest, which not only destroyed the wild animals but produced +great destruction of the domestic cattle as well. + +The _sleeping sickness_ has many features of interest. In the old +slavery days it was found that the negroes from the Congo region in +the course of the voyage or after they were landed sometimes were +affected with a peculiar disease. They were lethargic, took little +notice of their surroundings, slept easily and finally passed into a +condition of somnolence in which they took no food and gradually died. +There was no extension of the disease and it was attributed to extreme +homesickness and depression. A similar disease has been known for more +than one hundred years on the west coast of Africa, and attracted a +good deal of interest and curiosity on account of the peculiar +lethargy which it produced and from which it has received the name of +"sleeping sickness." Although apparently infectious in its native +haunts, it lost the power of spreading from man upon removal to +regions where it did not prevail. At first confined to a very small +region on the Niger river, it gradually extended with the development +of trade routes and the general increase of communications which trade +brings, until it prevails in the entire Congo basin, in the British +and German possessions in East Africa, and is extending north and +south of these regions. The cause of the disease and its mode of +conveyance was discovered in 1903. The fly _Glossina palpalis_ +which conveys the disease is a biting fly about the size of the common +house fly and lives chiefly in the vicinity of water. When such a fly +bites an individual who has sleeping sickness its bite can convey the +disease to monkeys, on whom the transmission experiments were made. +After biting the fly is infectious for a period of two days. After +this it is harmless, unless it again obtains a supply of living +trypanosomes. There is quite a period in which there are no symptoms +of the disease, although trypanosomes are found in the blood and in +the lymph nodes, and the individual is a source of infection. The +peculiar lethargy which has given the disease its name does not appear +until the nervous system is invaded by the parasites. It is impossible +to compute accurately the numbers of deaths from this disease--in the +region of Victoria Nyanza alone the estimates extend to hundreds of +thousands. + +3. In the third mode of insect conveyance the insect does not play a +merely passive role, but becomes a part of the disease, itself +undergoing infection, and a period in the life cycle of the organism +takes place within it. In all these cases quite a period of time must +elapse before the insect is capable of transmitting the disease; in +malaria, which is the best type of such a disease, this period is ten +days. Malaria is due to a small protozoan, the _Plasmodium +malariae_, which was discovered by Lavaran, a French investigator, +in 1882. The organism lives within or on the surface of the red blood +corpuscles. It first appears as a very minute colorless body with +active amoeboid movements, and increases in size, attacks a succession +of corpuscles, and finally attains a size as large as or larger than a +corpuscle. The corpuscles attacked become pale by the destruction of +haemoglobin, swell up and disintegrate, the haemoglobin becoming +converted into granules of black pigment inside the parasite. Having +attained a definite size the organism forms a rosette and divides into +a number of forms similar to the smallest seen inside the corpuscles; +these small forms enter other corpuscles and the cycle again begins. +This cycle of development takes place in forty-eight hours, and +segmentation is always accompanied by a paroxysm of the disease shown +in a chill followed by fever and sweating which is due to the effect +of substances liberated by the organism at the time of segmentation. A +patient may have two crops of the parasite developing independently in +the blood, and the two periods of segmentation give a paroxysm for +each, so that the paroxysms may appear at intervals of twenty-four +hours instead of forty-eight (Fig. 20). This cycle of development may +continue for an indefinite time, and there may be such a rapid +increase in the parasites as to bring about the death of the +individual; but with him the parasite would also perish, for there +would be no way of extending the infection and providing a new crop. +The disease has been transmitted by injecting the infected blood into +a normal individual. + +[Illustration: FIG. 20.--PART OF THE CYCLE OF DEVELOPMENT OF THE +ORGANISM OF MALARIA, _a-g_, Cycle of forty-eight hour development, the +period of chill coinciding with the appearance of _f_ and _g_ in the +blood. The organisms _g_, which result from segmentation, attack other +corpuscles and a new cycle begins. _h_, The male form or +microgametocyte, with the protruding and actively moving spermatozoa, +one of which is shown free. _i_ and _j_ are the macrogametes or female +forms. _k_ shows one of these in the act of being fertilized by the +entering spermatozooen. The differentiation into male and female forms +takes place in the blood, the further development of the sexual cycle +within the mosquito.] + +If a mosquito of the species _anopheles_ bites the affected +person, it obtains a large amount of blood which contains many +parasites. Within the mosquito the parasite undergoes a further +development into male and female sexual forms, which may also form in +the blood, termed respectively _microgametocyte_ and _macrogamete_. +From the microgametocyte small flagellate bodies, the male sexual +elements _microgametes_ or _spermatozoa_, develop and fertilize the +_macrogametes_; after fertilization this develops into a large body, +the _ooecyst_ which is attached to the wall of the stomach of the +mosquito. Within the ooecyst, innumerable small bodies, the +sporozoites, develop, make their way into the salivary glands and are +injected into the individual who becomes the prey of the mosquito, +and again the cycle of development begins. The presence of the +parasite within the mosquito does not constitute a disease. So far as +can be determined, life goes on in the usual way, and its duration in +the insect is not shortened. + +The nature of the parasite which produces yellow fever is unknown, for +it belongs to the filterable viruses; the infectious material, +however, has been shown by inoculation to exist in the blood, and the +disease is transmitted by a mosquito of another species, the +_stegomyia_. The development cycle within this takes a period of +twelve days, which time must elapse after the mosquito has bitten +before it can transmit the disease. Here again the mutual +interdependence of knowledge is shown. Nothing could have seemed less +useful than the study of mosquitoes, the differentiation of the +different species, their mode of life, etc., and yet without this +knowledge discoveries so beneficial and of such far-reaching +importance to the whole human race as that of the cause and mode of +transmission of malaria and yellow fever would have been impossible; +for it could easily have been shown that the ordinary _culex_ +mosquito played no role. The role which insects may play in the +transmission of disease was first shown by Theobald Smith in this +country, in the transmission by a tick of the disease of cattle known +as Texas fever. The infecting organism _pyrosoma bigenimum_ is a +tiny pear-shaped parasite of the red corpuscles. Smith's +investigations on the disease, published in 1893, is one of the +classics in medicine, and one of the few examples of an investigation +which has not been changed or added to by further work. + +One of the most interesting methods of extension of infection, showing +on what small circumstances infection may depend, is seen in the case +of the hookworm disease, which causes such devastation in the Southern +States. The organism which produces the disease, the _Uncinaria_, +belongs to the more highly developed parasites, and is a small round +worm one-third of an inch long. The worms which inhabit the intestines +have a sharp biting mouth by which they fasten themselves to the +mucous membrane and devour the blood. The most prominent symptom of +the disease is anaemia, or loss of blood, due not only to the direct +eating of the parasite, but to bleeding from the small wounds caused +by its bite. Large numbers of eggs are produced by the parasite which +are passed out with the feces, which becomes the only infectious +material. In a city provided with water-closets and a system of +sewerage there would be no means of extension of infection. The eggs +in the feces in conditions of warmth and moisture develop into small +crawling larvae which can penetrate the skin, producing inflammation of +this, known in the region as the ground itch. The larvae enter the +circulation and are carried to the lungs, where they perforate the +capillaries and reach the inner surface; from this they pass along the +windpipe, and then by way of the gullet and stomach reach their +habitat, the small intestine. Unfortunately, the habits and poverty of +the people in every way facilitate the extension of the infection. +There is no proper disposal of the feces, few of the houses have even +a privy attached to them, and the feces are distributed in the +vicinity of the houses. This leads to contamination of the soil over +wide areas. Most of the inhabitants of the country go barefoot the +greater part of the year, and this gives ready means of contact with +the larvae which crawl over the surface of the ground. The disease is +necessarily associated with poverty and ignorance, the amount of blood +is reduced to a low point, and industry, energy and ambition fall with +the blood reduction; the schools are few and inefficient; the children +are backward, for no child can learn whose brain cells receive but a +small proportion of the necessary oxygen; and a general condition of +apathy and hopelessness prevails in the effected communities. The +control of the disease depends upon the disinfection of the feces, or +at least their disposal in some hygienic method, the wearing of shoes, +and the better education of the people, all of which conditions seem +almost hopeless of attainment. The infection is also extended by means +of the negroes who harbor the parasite, but who have acquired a high +degree of immunity to its effects and whose hygienic habits are even +worse than those of the whites. The organism was probably imported +with the negroes from Africa and is one of the legacies of slavery. + +The diseases of animals are in many ways closely linked with those of +man. In the case of the larger parasites, such as the tapeworms and +the trichina, there is a direct interchange of disease with animals, +certain phases of the life cycle of the organisms are passed in man +and others in various of the domestic animals. A small inconspicuous +tapeworm inhabits the intestine of dogs and seems to produce no ill +effects. The eggs are passed from the dog, taken into man, and result +in the formation of large cystic tumors which not infrequently cause +death. Where the companionship between dog and man is very close, as +in Iceland, the cases are numerous. + +Most of the diseases in animals caused by bacteria and protozoa are +not transmitted to man, but there is a conspicuous exception. Plague +is now recognized as essentially an animal disease affecting rats and +other small rodents, and from these the disease from time to time +makes excursions to the human family with dire results. The greatest +epidemics of which we have any knowledge are of plague. In the time of +Justinian, 542 B.C., a great epidemic of plague extended over what was +then regarded as the inhabited earth. This pandemic lasted for fifty +years, the disease disappeared and appeared again in many places and +caused frightful destruction of life. Cities were depopulated, the +land in many places reverted to a wilderness, and the works of man +disappeared. The actual mortality cannot be known, but has been +estimated at fifty millions. Plague played a large part in the +epidemics of the Middle Ages. An epidemic started in 1346 and had as +great an extension as the Justinian plague, destroying a fourth of the +inhabitants of the places attacked; and during the fifteenth and +sixteenth and seventeenth centuries the disease repeatedly raised its +head, producing smaller and greater epidemics, the best known of +which, from the wonderful description of De Foe, is that of London in +1665, and called the Black Death. Little was heard of the disease in +the nineteenth century, although its existence in Asia was known. In +1894 it appeared in Hong Kong, extended to Canton, thence to India, +Japan, San Francisco, Mexico, and, in fact, few parts of the tropics +or temperate regions of the earth have been free from it. Mortality +has varied greatly, being greatest in China and in India; in the last +the estimate since 1900 is seven million five hundred thousand deaths. +The disease is caused by a small bacillus discovered in 1894 which +forms no spores and is easily destroyed by sunlight, but in the dark +is capable of living with undiminished virulence for an indefinite +time. The disease in man appears in two forms, the most common known +as bubonic plague, from the great enlargement of the lymph nodes, +those of the groin being most frequently affected. The more fatal form +is known as pneumonic plague, and in this the lungs are the seat of +the disease. + +In the old descriptions of the disease it was frequently mentioned +that large numbers of dead rats were found when it was prevalent, and +the most striking fact of the recent investigations is the +demonstration that the infection in man is due to transference of the +bacillus from infected rats. There are endemic foci of the disease +where it exists in animals, the present epidemic having started from +such a focus in Northern China, in which region the _Tarabagan_, +a small fur-bearing animal of the squirrel species, was infected. Rats +are easily infected, the close social habits of the animal, the vermin +which they harbor, and the habits of devouring their dead fellows +favor the extension of infection. The disease extends from the rat to +man chiefly by means of the fleas which contain the bacilli, and in +cases of pneumonic plague from man to man by means of sputum +infection. The disease once established in animals tends to remain, +the virus being kept alive by transmission from animal to animal, and +the persistence of the infection is favored by mild and chronic cases. + + + + +CHAPTER IX + +DISEASE CARRIERS.--THE RELATION BETWEEN SPORADIC CASES OF INFECTIOUS +DISEASE AND EPIDEMICS.--SMALLPOX.--CEREBRO-SPINAL +MENINGITIS.--POLIOMYELITIS.--VARIATION IN THE SUSCEPTIBILITY OF +INDIVIDUALS.--CONDITIONS WHICH MAY INFLUENCE SUSCEPTIBILITY.--RACIAL +SUSCEPTIBILITY.--INFLUENCE OF AGE AND SEX.--OCCUPATION AND +ENVIRONMENT.--THE AGE PERIOD OF INFECTIOUS DISEASES. + + +We have seen that insects serve as carriers of disease in two ways: in +one, by becoming contaminated with organisms they serve as passive +carriers, and in the other they undergo infection and form a link in +the disease. The more recent investigations of modes of transmission +of infectious diseases have shown that man, in addition to serving +while sick as a source of infection, may serve as a passive carrier in +two ways. For infection to take place not only must the pathogenic +organism be present, but it must be able to overcome the passive and +active defences of the body and produce injury. Pathogenic organisms +may find conditions favorable for growth on the surfaces of the body, +and may live there, but be unable to produce infection, and the +individual who simply harbors the organisms can transmit them to +others. Such an individual may be a greater source of infection than +one with the disease, because there is no suspicion of danger. The +organisms which thus grow on the surfaces have in some cases been +shown to be of diminished virulence, but in others have full +pathogenic power. Such passive carriers of infection have been found +for a number of diseases, as cerebro-spinal meningitis, diphtheria, +poliomyelitis and cholera. In all these cases the organisms are most +frequently found in those individuals who have been exposed to +infection as members of a family in which there have been cases of +disease. The other sort of carrier has had and overcome the disease, +but mutual relations have been established with the organism which +continues to live in the body cavity. Diphtheria bacilli usually +linger in the throat after convalescence is established, and until +they have disappeared the individual is more dangerous than one +actually sick with the disease. Health officers have recognized this +in continuing the quarantine against the disease until the organism +disappears. In typhoid fever bacilli may remain in the body for a long +time and be continually discharged, as in the well-known case of +"typhoid Mary."[1] + +Single cases of certain infectious diseases may appear in a community +year after year, and at intervals the cases become so numerous that +the disease is said to be epidemic. Such a disease is smallpox. This +is a highly infectious disease, towards which all mankind is +susceptible. Complete protection against the disease can be conferred +by Jenner's discovery of vaccination. The disease becomes modified +when transferred to cattle, producing what is known as cowpox, in +which vesicles similar to those of smallpox appear on the skin. The +inoculation of man with the contents of such a vesicle produces a mild +form of disease known as vaccinia, which protects the individual from +smallpox. This protection is fully as adequate as that produced by an +attack of smallpox, and we are warranted in saying that if thorough +vaccination, or the inoculation with vaccinia, were carried out +smallpox would disappear. There are great difficulties in the way of +carrying out effective vaccination of the whole population, which are +accentuated by the active opposition of people who are ignorant and +wilfully remain so. There exists in every state a number of people +unprotected by vaccination, and among these single cases of smallpox +appear. The unprotected individuals gradually increase in number, +forming an inflammable material awaiting the spark or infection which +produces a conflagration in the one case and an epidemic in the other. + +Cerebro-spinal meningitis is another example of a disease which exists +in sporadic and epidemic form. This disease is caused by a small +micrococcus, the organisms joined in pairs. The seat of the disease is +in the meninges or membranes around the brain and spinal cord. The +micrococci enter the body from the throat and nose, and either pass +directly from here into the meninges, or they enter into the blood and +are carried by this into the meninges. The organisms are easily +destroyed and cannot long survive the conditions outside the body, so +that for infection to take place the transmission must be very direct. +Carriers who have the organisms in the throat, but who do not have the +disease, are the principal agents in dissemination. The mortality is +high, and even in recovery permanent damage is often done to the brain +or to the organs of special sense. Sporadic cases constantly occur in +small numbers, and it is difficult or impossible to trace any +connection between these cases. At varying intervals, often twenty +years intervening, an epidemic appears which sometimes remains local +in a city or state, sometimes extends to adjoining cities or states, +and may even extend over a very large area. In the epidemics the +mortality is much higher than in the sporadic cases. The same +explanation given for smallpox cannot apply here, for there is not a +similar accumulation of susceptible material. We know there is a great +deal of variation in the virulence of the different pathogenic +organisms, and the virulence can be artificially increased and +diminished. In epidemics of meningitis the virulence of the organisms +is increased, as is shown by the greater mortality. It is highly +probable that such epidemics are due to changes which arise in the +organisms from causes we do not know and which increase their capacity +for harm. It is possible that such a change would convert a carrier +into a case of disease, the organism acquiring greater powers of +invasion. Such a strain of organisms arising in one place and +producing an epidemic could be transported to another locality and +exert the same action, or similar changes in the organisms could arise +simultaneously in a number of places. Analogies to such conditions are +given in plants. In certain plants it has been shown that from unknown +causes there appears a tendency to the production of variations. A +very beautiful herbaceous peony known as "Bridesmaid" after having +grown for a number of years in single form, in one year wherever grown +suddenly became double. The peculiar thing with the lower unicellular +organisms is that the changes which so arise do not tend to become +permanent, the organism reverts to its usual character, the disease to +its sporadic type. + +A very fatal form of poliomyelitis has for a number of years prevailed +in Sweden. In the United States there have been continually a number +of single cases of the disease, and it is not impossible that a more +pathogenic strain of the organism has developed in Sweden and has been +imported into this country, giving rise to the much greater extension +of the disease in a number of places. + +The most cursory study of the infectious diseases shows that there is +great variation in the susceptibility of individuals. Even in the most +severe epidemics all are not equally affected, some escape the +infection, others have the disease lightly, others severely, some die. +Chance enters into this, but plays a small part, for the same varying +individual susceptibility is shown experimentally. If a given number +of animals of the same species, age and weight, even those from the +same litter, be inoculated with a given number of bacteria shown to be +pathogenic for that species, the results differ. If the dose be +necessarily fatal, death will take place at intervals; if a dose +smaller than the fatal be used, some animals will die, others will +recover. The defences of the organism being centred in the activity of +the living tissue, any condition which depresses cell activity may +have an effect in increasing susceptibility to infection. Animals +which ordinarily are not susceptible to infection with a certain +organism may be made so by prolonged hunger, or fatigue, by the +influence of narcotics, by reduction of the body temperature, by loss +of blood. In man prolonged fatigue, cold, the use of alcohol to excess +and even psychic depression increases susceptibility. It has been +shown that such conditions are accompanied by a diminution in the +power of the blood to destroy bacteria. + +There is variation in the susceptibility to infection in the different +races of man. If a race be confined to one habitat with close +intercourse between the people, such a race may acquire a high degree +of immunity to local diseases by a gradual weeding out of the +individuals who are most susceptible. A degree of comparative harmony +may be gradually established between host and parasite, as is the case +in wild animals. These have few diseases, the weak die, the resistant +breed; they harbor, it is true, large numbers of parasites, but there +is mutual adjustment between parasite and host. Diseases in animals +greatly increase under the artificial conditions of domestication. +Certain highly specialized breeds of cattle, as the Alderneys, are +much more susceptible to tuberculosis than the less specialized. The +high development of the variation which consists in a marked ability +to produce milk fat is probably combined with other qualities, shown +in diminished resistance to disease, and under natural conditions the +variation would not have persisted. The introduction of a new disease +into an isolated people has often been attended with dire +consequences. It is much the same thing with the introduction of +disease of plants. In Europe the brown-tail moth and the gypsy moth +produce continuously a certain amount of damage to the trees, but +their parasitic enemies have developed with them and check their +increase. These pests were brought to this country in which there were +no conditions retarding their increase and have produced great damage. + +It is very difficult to estimate the degree of racial susceptibility. +The negro race seems to be more susceptible to certain diseases, such +as tuberculosis and smallpox, less so to others, as yellow fever, +malaria and uncinariasis. What are apparently differences in +susceptibility may be explained by racial customs. A statistical +inquiry into death in India from poisonous snakes might be interpreted +as showing a marked resistance on the part of the white to the action +of the venom, but it is merely a question of the boots of the whites +and the naked feet and legs of the natives. The relatively greater +frequency of smallpox in the blacks is due to the greater difficulties +in carrying out vaccination measures among them and the greater +opportunity for infection which results from their less hygienic life. +It has always been noted that when plague prevails in Oriental cities, +the natives are more frequently attacked than are Europeans. This does +not depend upon differences in susceptibility, but on the better +hygienic conditions of the whites which prevent the close relation to +rats and vermin by which infection is extended. There would be but +little extension of the hookworm disease in a community where shoes +were worn and the habits were cleanly. + +It is by no means improbable that the formation of the habits of +civilization was influenced by infection. Most of these habits, such +as personal cleanliness, the avoidance of close contact, the demand +for individual utensils for eating and drinking, are all of distinct +advantage in opposing infection. Certain habits, on the other hand, +such as kissing, which probably represents the extension of a habit of +sexual origin, are disadvantageous and infection is often transmitted +in this way. In syphilitic infection the mouth forms one of the most +common localizations of the disease and may contain the causal +organisms in great numbers. This, the _spirochaeta pallida_, is an +organism of great virulence, and man is the most susceptible animal. +The disease, like gonorrhoea, is essentially a sexual disease, the +primary location is in the sexual organs, and it is transmitted +chiefly by sexual contact. Of all the infectious diseases, it is the +one most frequently transmitted to the unborn child; in certain cases +the disease is transmitted, in others the developing foetus may be so +injured by the toxic products of the disease that various +imperfections of development result, as is shown in deformities, or in +conditions which render the entire organism or individual organs, +particularly the nervous system, more susceptible to injury. Following +the primary localization of the acquired form of the disease, there is +usually secondary localization in the mucous membrane of the mouth, +and the disease may be transmitted by kissing or by the use of +contaminated utensils. The habit of indiscriminate kissing is one +which might with great benefit be given up. + +There is definite relation between age and the infectious diseases. In +general, susceptibility is increased in the young; young animals can +be successfully inoculated with diseases to which the adults of the +species are immune, and certain human diseases, such as scarlet fever, +measles and whooping cough, seem to be the prerogatives of the child. +It must be remembered, however, that one attack of these diseases +confers a strong and lasting immunity and children represent a raw +material unprotected by previous disease. Where measles has been +introduced into an island population for the first time, all ages seem +equally susceptible. All ages are equally susceptible to smallpox, and +yet in the general prevalence of the disease in the prevaccination +period it was almost confined to children, the adults being protected +by a previous attack. The habits and environment at different ages +have an influence on the opportunities for infection. There is +comparatively little opportunity for infection during the first year, +in which period the infant is nursed and has a narrow environment +within which infection is easily controlled. With increasing years the +opportunities for infection increase. When the child begins to move +and crawl on hands and knees the hands become contaminated, and the +habit of putting objects handled into the mouth makes infection by +this route possible. Food also becomes more varied, milk forms an +important part of the diet, and we are now appreciating the +possibilities of raw milk in conveying infection. With the enlarging +environment, with the school age bringing greater contact of the child +with others, there come greater opportunities for infection which are +partly offset by the increase in cleanliness. The dangers of infection +in the school period are now greatly lessened by medical inspection +and care of the school children. In the small epidemic of smallpox +which prevailed in Boston from 1881 to 1883, there was a sharp decline +in the incidence of the disease in children as soon as the school age +was reached, this being due to the demand of vaccination as a +condition for entrance into the schools. Many of the infectious +diseases are much milder in children than in adults. This is the case +in typhoid fever, malaria and yellow fever. The comparative immunity +of the natives to yellow fever in regions where this prevails seems to +be due to their having acquired the disease in infancy in so mild a +form that it was not recognized as such. + +The infectious diseases are preeminently the diseases of the first +third of life. After the age of forty man represents a select +material. He has acquired immunity to many infections by having +experienced them. Habits of life have become fixed and there is a +general adjustment to environment. The only infectious disease which +shows no abatement in its incidence is pneumonia, and the mortality in +this increases with age. Between thirty-five and fifty-five man stands +on a tolerably firm foundation regarding health; after this the age +atrophies begin, the effects of previous damage begin to be apparent, +and the tumor incidence increases. + +FOOTNOTE: +[1] This was the case of a woman, by occupation a cook, whose numerous +exchanges of service were accompanied by the appearance of cases of +typhoid fever in the families. This became so marked that an +examination was made and she was found to be a typhoid carrier and as +such constantly discharging typhoid bacilli. She is now isolated. + + + + +CHAPTER X + +INHERITANCE AS A FACTOR IN DISEASE.--THE PROCESS OF CELL +MULTIPLICATION.--THE SEXUAL CELLS DIFFER FROM THE OTHER CELLS OF THE +BODY.--INFECTION OF THE OVUM.--INTRA-UTERINE INFECTION.--THE PLACENTA +AS A BARRIER TO INFECTION.--VARIATIONS AND MUTATIONS.--THE INHERITANCE +OF SUSCEPTIBILITY TO DISEASE.--THE INFLUENCE OF ALCOHOLISM IN THE +PARENTS ON THE DESCENDANTS.--THE HEREDITY OF NERVOUS +DISEASES.--TRANSMISSION OF DISEASE BY THE FEMALE ONLY.--HEMOPHILIA.-- +THE INHERITANCE OF MALFORMATIONS.--THE CAUSES OF +MALFORMATIONS.--MATERNAL IMPRESSIONS HAVE NO INFLUENCE.--EUGENICS. + + +The question of inheritance of disease is closely associated with the +study of infection, and the general subject of heredity in its bearing +on disease can be considered here. By heredity is understood the +transference of similar characteristics from one generation of +organisms to another. The formation of the sexual cells is a much more +complex process than that of the formation of single differentiated +cells, for the properties of all the cells of the body are represented +in the sexual cells, to the union of which the heredity transmission +of the qualities of the parents is due. In the nucleus of all the +cells in the body there is a material called _chromatin_, which +in the process of cell division forms a convoluted thread; this +afterwards divides into a number of loops called _chromosomes_, +the number of which are constant for each animal species. In cell +division these loops divide longitudinally, one-half of each going to +the two new cells which result from the division; each new cell has +one-half of all the chromatin contained in the old and also one-half +of the cytoplasm or the cell material outside of the nucleus. The +process of sexual fertilization consists in the union of the male and +female sex cells and an equal blending of the chromatin contained in +each (Fig. 22). In the process of formation of the sexual cells a +diminution of the number of chromosomes contained in them takes place, +but this is preceded by such an intimate intermingling of the +chromatin that the sexual cells contain part of all the chromosomes of +the undifferentiated cells from which they were formed. The new cell +which is formed by the union of the male and female sexual cells and +which constitutes a new organism, contains the number of chromosomes +characteristic of the species and parts of all the chromatin of the +undifferentiated cells of male and female ancestors. As a result of +this the most complicated mechanism in nature, it is evident that in a +strict sense there can be no heredity of a disease because heredity in +the mammal is solely a matter of the chromosomes and these could not +convey a parasite. The new organism can, however, quickly become +diseased and, by the transference of disease to it and by either +parent, there is the appearance of hereditary transmission of disease, +though in reality it is not such. The ovum itself can become the site +of infection; this, which was first discovered by Pasteur in the eggs +of silkworms, takes place not infrequently in the infection of insects +with protozoa. In Texas fever the ticks which transmit the disease, +after filling with the infected blood, drop off and lay eggs which +contain the parasites, and the disease is propagated by the young +ticks in whom the parasites have multiplied. The same thing is true in +regard to the African relapsing or tick fever, which is also +transferred by a tick. In the white diarrhoea of chickens the eggs +become infected before they are laid and the young chick is infected +before it emerges from the shell. It is highly improbable, and there +is no certain evidence for it, that the extremely small amount of +material contributed by the male can become infected and bring +infection to the new organism. In the cases in which disease of the +male parent is transferred to the offspring, it is either by an +infection of the female by the male, with transference of the +infection from her to the developing organism, or with the male sexual +cells there may be a transference to the female of the infectious +material and the new organism may be directly infected. No other +disease in man is so easily and directly transferred from either +parent to offspring as is syphilis, and the disease is extremely +malignant for the foetus, usually causing death before the normal +period of intra-uterine development is reached. + +[Illustration: FIG. 21.--DIAGRAM SHOWING THE RELATION OF THE SEXUAL +CELLS TO THE SOMATIC CELLS OR THOSE OF THE GENERAL BODY. The sexual +cells are represented to the left of the line at the bottom of diagram +and are black. From the fertilized ovum at the top there is a +continuous cell development, with differentiation represented in the +cell groups of the bottom row. It is seen that the sexual cells are +formed directly from the germ cell and contain no admixture from the +cells of the body.] + +The mother gives the protection of a narrow and unchanging environment +and food to the new organism which develops within the uterus, and +there is always a membranous separation between them. Disease of the +mother may affect the foetus in a number of ways. In most cases the +membrane of separation is an efficient guard preventing pathogenic +organisms reaching the foetus from the mother. In certain cases, +however, the guard can be passed. In smallpox, not infrequently, the +disease extends from the mother to the foetus, and the child may die +of the infection or be born at term with the scars resulting from the +disease upon it. Syphilis in the mother in an active stage is +practically always extended to the foetus. We have said that in an +infectious disease substances of an injurious character are produced +by bacteria, and such substances being in solution in the blood of the +infected mother can pass through the membranous barrier and may +destroy the foetus although the mother recovers from the infection. + +[Illustration: FIG. 22.--DIAGRAMMATIC REPRESENTATION OF THE PROCESS OF +FERTILIZATION. (Boveri.) In the first cell (_a_) the ovum is shown in +process of fertilization by the entering spermatozoon or male sexual +element. In the following cells there is shown the increase in amount +of the male material and the final intimate commingling in _g_ which +precedes the first segmentation. _g_ represents a new organism formed +by the union of the male or female cell but differing from either of +them.] + +Living matter is always individual, and this individuality is +expressed in slight structural variations from the type of the species +as shown in an average of measurements, and also in slight variations +in function or the reactions which living tissue shows towards the +conditions acting upon it. The anatomical variations are more striking +because they can be demonstrated by weight and measure, but the +functional variations are equally numerous. Thus, no two brains react +in exactly the same way to the impressions received by the sense +organs; there are differences in muscular action, differences in +digestion; these variations in function are due to variations in the +structure of living material which are too minute for our +comparatively coarse methods of detection. In the enormous complexity +of living matter it is impossible that there should not be minute +differences in molecular arrangement and to this such functional +variations may be due. Chemistry gives us a number of examples of +variations in the reaction of substances which with the same +composition differ in the molecular arrangement. Even in so simple a +mechanism as a watch there are slight differences in structure which +gives to each watch certain individual characteristics, but the type +as an instrument constructed for recording time remains. In the fusion +of the chromosomes of the male and female sexual cells, to which the +hereditary transmission of the ancestral qualities to the new +offspring is due, there are differences in the qualities of each, for +the individuality of the parents is expressed in the germ cells, and +the varying way in which these may fuse gives to the new cell +qualities of its own in addition to qualities which come from each +ancestor, and from remote ancestors through these. The qualities with +which the new organism starts are those which it has received from its +ancestors plus its individuality. The fact that the sexual cells are +formed from the early formed cells of the new organism which represent +all of the qualities of the fertilized ovum or primordial cell, +renders it unlikely that the new offspring will contain qualities +which the parents have acquired. The question of the inheritance of +characteristics which the parents have acquired as the result of the +action of environment upon them is one which is still actively +investigated by the students of heredity, but the weight of evidence +is opposed to this belief. + +In the new organism the type of the species is preserved and the +variations from the mean to which individuality is due are slight. We +are accustomed to regard as variations somewhat greater departures +from the species type than is represented in individuality, but there +is no sharp dividing line between them. + +Very much wider departures from the species type are known as +mutations. Such variations and mutations, like individuality, may be +expressed in qualities which can be weighed and measured, or in +function, and all these can be inherited; certain of them known as +dominant characteristics more readily than others, which are known as +recessive. If these variations from the type are advantageous, they +may be preserved and become the property of the species, and it is in +this way that the characteristics of the different races have arisen. +Certain of the variations are unfavorable to the race. The varying +predisposition to infection which undoubtedly exists and may be +inherited represents such a variation. Tuberculosis is an instance of +this; for, while the cause of the disease is the tubercle bacillus, +there is enormous difference in the resistance of the body to its +action in different individuals. The disease is to a considerable +extent one of families, but while this is true the degree of the +influence exerted by heredity can be greatly overestimated. The +disease is so common that in tracing the ancestry of tuberculous +patients it is rare to find the disease not represented in the +ancestors. A further difficulty is that the environment is also +inherited. The child of a tuberculous parent has much better +opportunity to acquire the infection than a child without such an +environment [page 167]. Other diseases than the infectious seem to be +inherited, of which gout is an example. In gout there is an unusual +action of the cells of the body which leads to the formation and the +retention in the body of substances which are injurious. Here it is +not the disease which is inherited, but the variation in structure to +which the unusual and injurious action of the cells is due. + +While tuberculosis and gout represent instances in which, although the +disease itself is not inherited yet the presence of the disease in the +ascendants so affects the germinal material that the offspring is more +susceptible to these particular diseases, much more common are the +cases in which disease in the parents produces a defective offspring, +the defect consisting in a general loss of resistance manifested in a +variety of ways, but not necessarily repeating the diseased condition +of the parent. In these cases the disease in the parents affects all +the cells of the body including the germinal cells, and the defective +qualities in the germ cells will affect the cells of the offspring +which are derived from these. There is a tendency in these cases to +the repetition in the offspring of the disease of the parents, because +the particular form of the parental disease may have been due to or +influenced by variation of structure. One of the best examples of +affection of the offspring by diseased conditions of the parents +produced by a toxic agent which directly or indirectly affects all the +cells of the body is afforded by alcohol when used in excess. Since +drunkenness has become a medical rather than a moral question, a great +deal of reliable data has accumulated in regard to it as a factor in +the heredity of disease. Grotjahn gives the following examples: Six +families were investigated in which there were thirty-one children. In +all these families the father and grandfather on the father's side +were chronic alcoholics, and in certain of the families drunkenness +prevailed in the more remote ancestors. The following was the fate of +the children: eight died shortly after birth of general weakness, +seven died of convulsions in the first month, three were malformed, +three were idiotic, three were feeble-minded, three were dwarfs, three +were epileptics, two were normal. In a second group of three families +there were twenty children. The fathers were drunkards, but their +immediate ancestors were free: four children died of general weakness, +three of convulsions in the first month, two were feeble-minded, one +was a dwarf, one was an epileptic, seven were normal. In a family in +which both father and mother and their ancestors were drunkards there +were six children: three died of convulsions within six months, one +was an idiot, one a dwarf, and one an epileptic. For comparison there +were taken from the same station in life ten families in which there +was no drunkenness: three children died from general weakness, three +from intestinal troubles, two of nervous affection, two were +feeble-minded, two were malformed, fifty were normal. Legrain has +studied on a larger scale the descendants of two hundred and fifteen +families of drunkards in which there were eight hundred and nineteen +children. One hundred and forty-five of these were insane, sixty-two +were criminals, and one hundred and ninety-seven drunkards. Of course +all this cannot be attributed to alcohol alone. There is first to be +considered a probable variation in the nervous system which is +expressed in the alcoholic habit; second, the environment consisting +in poverty, bad associates, etc., which the alcoholic habit brings; +third, the alcohol alone. That defective inheritance so frequently +takes the form of alcoholism is largely due to the environment. There +has never been the opportunity to study on a large scale the effect of +the complete deprivation of alcohol from a people living in the +environment of modern civilization. There is a possibility, and even +probability, that the defective nervous organization which predisposes +to alcoholism would seek satisfaction in the use of some other +sedative drug. So complex are all the interrelations of the social +system that it would be possible to regard alcohol as an agent useful +in removing the defective, were it not for its long-enduring action +and its effects on the descendants, procreation not being affected by +its use. + +Diseases of the nervous system are particularly apt to affect the +offspring, and often the inherited condition repeats that of the +parents. This is due to the fact that most of the nervous diseases +depend both upon intrinsic factors which consist in some defective +condition of the nervous system representing a variation, and +extrinsic factors due to environment or occupation which make the +basal condition operative. The definite relation between alcoholism +and insanity is due to alcohol acting not as an intrinsic but an +extrinsic factor, bringing into effectiveness the hereditary weakness +of the nervous system. The influence of heredity in producing insanity +is variously estimated at from twenty-six per cent to sixty per cent +of all cases. This great difference in the estimation of the +hereditary influence is due to the personal equation of the +statistician, and the care with which other factors are eliminated. In +the more severe form of the hereditary degeneration the same +pathological conditions are repeated in the descendants. In certain +cases the severity of the condition increases from generation to +generation. According to Morel there may be merely what is recognized +as a nervous temperament often associated with moral depravity and +various excesses in the first generation; in the second, severe +neuroses, a tendency to apoplexy and alcoholism; in the third, psychic +disturbances, suicidal tendencies and intellectual incapacity; and in +the fourth, congenital idiocy, malformations and arrests of +development. There are some very definite data with regard to +inheritance in the nervous disease known as epilepsy. The essential +condition in this consists in attacks of unconsciousness, usually +accompanied by a discharge of nerve force shown in convulsions, the +attack being often preceded by peculiar sensations of some sort known +as the aura. In the most marked forms of the affection heredity plays +but little part, owing to the early supervention of imbecility and +helplessness, and it is a greater factor in the better classes of +society than in the proletariat. In the better classes, owing to the +greater care of the cases and the avoidance of exciting causes of the +attacks, the disease is better controlled and rarely advances to the +extent that it does among the poor. The association of epilepsy and +alcoholism is especially dangerous, for a slight amount of alcohol may +greatly accentuate the disease. In five hundred and thirty-five +children in whose parentage there were sixty-two male and seventy-four +female epileptics, twenty-two were born dead, one hundred and +ninety-five died from convulsions in infancy, twenty-seven died in +infancy from other causes, seventy-eight were epileptics, eleven were +insane, thirty-nine were paralyzed, forty-five were hysterical, six +had St. Vitus's dance, one hundred and five were ordinarily healthy. +That variations in the nervous system which produce more or less +unusual mental peculiarities and which do not take the form of nervous +disease are inherited, the most superficial consideration shows. A +child in its mental characteristics is said to take after one or the +other of its parents, certain habits and mental traits are the same, +often even the handwriting of a child resembles that of a parent. + +In certain cases the inheritance is transmitted by the female alone. +This is the case in the haemophilia, the unfortunate subjects of which +are known as bleeders. There is in this a marked tendency to +haemorrhage which depends upon an alteration in the character of the +blood which prevents clotting. This, the natural means of stopping +bleeding from small wounds, being in abeyance, fatal haemorrhage may +result from pulling a tooth or from an insignificant wound. There is a +seeming injustice in the inheritance, for the females do not suffer +from the disease although they transmit it, while the males who have +the disease cannot even create additional sympathy by transmitting it. + +The most obvious inheritance is seen in the case of malformations. +These represent wide departures from the type of the species as +represented in the form. There is no hard and fast line separating the +slight departures from the normal type known as variations and +mutations, from the malformations. Certain of the malformations known +as monstrosities hardly represent the human type. These are the cases +in which the foetus is represented in a formless mass of tissue, or +there is absence of development of important parts such as the nervous +system or there is more or less extensive duplication of the body. +There has always been a great deal of popular interest attached to the +malformations owing to the part which maternal impressions are +supposed to play in their production. In this, some striking +impression made on the pregnant woman is supposed to affect in a +definite way the structure of the child. The cases, for instance, in +which a woman sees an accident involving a wound or a loss of an arm +and the child at birth shows a malformation involving the same part. +There is no association between maternal impressions and +malformations, although there have been many striking coincidences. +All malformations arise during the first six weeks of pregnancy known +as the embryonic period, in which the development of the form of the +child is taking place, and during which time there is little +consciousness of pregnancy. Maternal impressions are usually received +at a later period, when the form of the child is complete and it is +merely growing. It must be remembered also that there is neither +nervous nor vascular connection between the child in the uterus and +the mother, the child being from the period of conception an +independent entity to which the mother gives nutriment merely. Of +course, as has been said, the mother may transmit to the child +substances which are injurious, and in certain cases parasites may +pass from the mother to the foetus. The same types of malformations +which occur in man are also seen in birds, and it would require a more +vigorous imagination than is usual to believe that a brooding hen +could transmit an impression to an egg and that a headless chick could +result from witnessing the sacrifice of an associate. The idea of the +importance of maternal impressions in influencing the character of the +offspring is a very old one, a well-known instance being the sharp +practice of Jacob's using peeled wands to influence the color of his +cattle. In regard to coincidences the great number of cases in which +strong impressions made on the mind of the pregnant mother without +result on the offspring are forgotten. The belief has been productive +of great anxiety and even unhappiness during a period which is +necessarily a trying one, and should be dismissed as being both +theoretically impossible and unsupported by fact. + +The malformations are divided anatomically into those characterized, +first, by excess formation, second, by deficient formation, third, by +abnormal displacement of parts. They are due to intrinsic causes which +are in the germ, and which may be due to some unusual conditions in +either the male or female germ cell or an imperfect commingling of the +germinal material, and to extrinsic causes which physically, as in the +nature of a shock or chemically as by the action of a poison, may +affect the embryo through the mother. Malformations are made more +numerous in chickens by shaking the eggs before brooding. A number of +malformations are produced by accidental conditions arising in the +environment; for instance, the vascular cord connecting mother and +child may become wound around parts constricting them or even cutting +them off, and the membrane around the child may become adherent to +certain parts and prevent the development of these. The extrinsic +causes are more operative the more unfavorable is the environment of +the mother. Malformations are more common in illegitimate children +than in legitimate and more common in alcoholic mothers; there is an +unfavorable environment of poverty in both cases, added to in the +latter and usually in the former by the injurious action of the +alcohol. + +The more extensive malformations have no effect on heredity, because +the subjects of them are incapable of procreation. The malformations +which arise from the accidents of pregnancy and which are compatible +with a perfectly normal germ are in the nature of acquired +characteristics and are not inherited. Those malformations, however, +which are due to qualities in the germinal material itself are +inherited, and certain of them with remarkable persistence. There are +instances in which the slight malformation consisting in an excess of +fingers or toes has persisted through many generations. It may +occasionally lapse in a generation to reappear later. In certain +cases, notably in the bleeders, the inheritance is transmitted by the +female alone, in other cases by the sexes equally, but there are no +cases of transmission by the male line only. It is evident that when +the same malformation affects both the male and the female line the +hereditary influence is much stronger. A case has been related to me +in which most of the inhabitants in a remote mountain valley in +Virginia where there has been much intermarriage have one of the +joints of the fingers missing. There is a very prevalent idea that in +close intermarriage in families variations and malformations often +unfortunate for the individual are more common. All experimental +evidence obtained by interbreeding of animals shows that close +interbreeding is not productive of variation, but that variations +existing in the breed become accentuated. Variations either +advantageous or disadvantageous for the race or individual may either +of them become more prevalent by close intermarriage. It seems, +however, to have been shown by the customs of the human race that very +close intermarriage is disadvantageous. + +Eugenics, which signifies an attempt at the betterment of the race by +the avoidance of bad heredity, has within recent years attracted much +attention and is of importance. Some of its advocates have become so +enthusiastic as to believe that it will be possible to breed men as +cattle and ultimately to produce a race ideally perfect. It is true +that by careful selection and regulation of marriage certain +variations, whether relating to coarse bodily form or to the less +obvious changes denoted by function, can be perpetuated and +strengthened. That the Semitic race excels in commerce is probably due +to the fact that the variation of the brain which affected favorably +the mental action conducive to this form of activity, was favorable +for the race in the hostile environment in which it was usually placed +and transmitted and strengthened by close intermarriage. It is +impossible, however, to form a conception of what may be regarded as +an ideal type of the human species. The type which might be ideal in a +certain environment might not be ideal in another, and environment is +probably of equal importance with the material. The eugenics movement +has enormously stimulated research into heredity by the methods both +of animal experimentation and observation, and study of heredity in +man. As in all of the beginning sciences there is not the close +inter-relation of observed facts and theory, but there is excess of +theory and dearth of facts. Certain considerations, however, seem to +be evident. It would seem to be evident that individuals should be +healthy and enabled to maintain themselves in the environment in which +they are placed, but the qualities which may enable an individual +successfully to adapt himself to factory life, or life in the crowds +and strong competition of the city, may not be, and probably are not, +qualities which are good for the race in general or for his immediate +descendants. At present our attempts to influence heredity should be +limited to the heredity of disease only. We can certainly say that +intermarriage between persons who have tuberculosis or in whose +families the disease has prevailed is disadvantageous for the +offspring; the same holds true for insanity and for nervous diseases +of all sorts, for forms of criminality, for alcoholism, and for those +diseases which are long enduring and transmitted by sexual contact +such as syphilis and gonorrhoea. It is of importance that the facts +bearing on the hereditary transmission of disease should become of +general knowledge, in order that the dangers may be known and +voluntarily avoided. No measures of preventive medicine are successful +which are not supported by a public educated to appreciate their +importance, and the same holds true of eugenics. How successful will +be public measures leading to the prevention of offspring in the +obviously unfit by sterilization of both males and females is +uncertain. It is doubtful whether public sentiment at the present time +will allow the measure to be thoroughly carried out. Some results in +preventing unfit heredity may be attained by the greater extension of +asylum life, but the additional burden of this upon the labor of the +people would be difficult to bear. At best such measures would only be +carried out in the lower class of society. + + + + +CHAPTER XI + +CHRONIC DISEASES.--DISEASE OF THE HEART AS AN EXAMPLE.--THE STRUCTURE +AND FUNCTION OF THE HEART.--THE ACTION OF THE VALVES.--THE PRODUCTION +OF HEART DISEASE BY INFECTION.--THE CONDITIONS PRODUCED IN THE +VALVES.--THE MANNER IN WHICH DISEASE OF THE VALVES INTERFERES WITH +THEIR FUNCTION.--THE COMPENSATION OF INJURY BY INCREASED ACTION OF +HEART.--THE ENLARGEMENT OF THE HEART.--THE RESULT OF IMPERFECT WORK OF +THE HEART.--VENOUS CONGESTION.--DROPSY.--CHRONIC DISEASE OF THE +NERVOUS SYSTEM.--INSANITY.--RELATION BETWEEN INSANITY AND +CRIMINALITY.--ALCOHOLISM AND SYPHILIS FREQUENT CAUSES OF +INSANITY.--THE DIRECT AND INDIRECT CAUSES OF NERVOUS DISEASES.--THE +RELATION BETWEEN SOCIAL LIFE AND NERVOUS DISEASES.--FUNCTIONAL AND +ORGANIC DISEASE.--NEURASTHENIA. + + +Chronic diseases are diseases of long duration and which do not tend +to result in complete recovery; in certain cases a cause of disease +persists in the body producing constant damage, or in the course of +disease some organ or organs of the body are damaged beyond the +capacity of repair, and the imperfect action of such damaged organs +interferes with the harmonious inter-relation of organs and the +general well-being of the body. The effect of damage in producing +chronic disease may not appear at once, for the great power of +adaptation of organs and the exercise of reserve force may for a time +render the damage imperceptible; when, however, age or the +supervention of further injury diminishes the power of adaptation the +condition of disease becomes evident. Chronic disease may be caused by +parasites when the relation between host and parasite is not in high +degree inimical, as in tuberculosis, gonorrhoea, syphilis, most of the +trypanosome diseases and the diseases produced by the higher +parasites. In certain cases the chronic disease represents really a +series of acute onsets; thus in the case of the parasites there may be +periods of complete quiescence of infection but not recovery, the +parasites remaining in the body and attacking when the defences of the +body are in some way weakened. In such cases there may be temporary +immunity produced by each excursion of the disease, but the immunity +is not permanent nor is the parasite destroyed. There is a further +connection between chronic disease and infection in that the damage to +the organs, which is the great factor underlying chronic disease, is +so often the result of an infection. + +The infectious diseases are those of early life; chronic disease, on +the other hand, is most common in the latter third of life. This is +due to the fact that in consequence of the general wear of the body +this becomes less resistant, less capable of adaptation, and organic +injury, which in the younger individual would be in some way +compensated for, becomes operative. The territory of chronic disease +is so vast that not even a superficial review of the diseases coming +under this category can be attempted in the limits of this book, and +it will be best to give single examples only, for the same general +principles apply to all. One of the best examples is given in chronic +disease of the heart. + +The heart is a hollow organ forming a part of the blood vascular +system and serving to give motion to the blood within the vessels by +the contraction of its strong muscular walls. It is essentially a +pump, and, as in a pump, the direction which the fluid takes when +forced out of its cavity by the contraction of the walls diminishing +or closing the cavity space, is determined by valves. The contraction +of the heart, which takes place seventy to eighty times in a minute, +is automatic and is due to the essential quality of the muscle which +composes it. The character, frequency and force of contraction, +however, can be influenced by the nervous system and by the direct +action of substances upon the heart muscle. The heart is divided by a +longitudinal partition into a right and left cavity, and these +cavities are divided by transverse septa, with openings in them +controlled by valves, each into two chambers termed _auricle_ and +_ventricle_. The auricle and ventricle on each side are +completely separated. + +The circulation of the blood through the heart is as follows: The +blood, which in the veins of the body is flowing towards the heart, +passes by two channels, which respectively receive the blood from the +upper and lower part of the body, into the right auricle. When this +becomes distended it contracts, forcing the blood into the right +ventricle; the ventricle then contracts and sends the blood into the +arteries of the lungs, the passage of blood into the auricle being +prevented by valves which close the opening between auricle and +ventricle when the latter contracts upon its contents. When the +ventricle empties by its contraction the wall relaxes and the back +flow from the artery is prevented by crescentic-shaped valves placed +where the artery joins the ventricle. A similar arrangement of valves +is on the left side of the heart. The pressure given the blood by the +contraction of the right ventricle sends it through the lungs; from +these, after it has been oxygenated, it passes into the left auricle, +then into the left ventricle and from this into the great artery of +the body, the aorta, which gives off branches supplying the +capillaries of all parts of the body. Both of the auricles and both of +the ventricles contract at the same, time, the ventricular contraction +following closely upon the contraction of the auricles. Contraction or +systole is followed by a pause or diastole during which the blood +flows from the veins into the auricles. The work which the right +ventricle accomplishes is very much less than that of the left, and +the right ventricle has a correspondingly thinner wall. The size of +the heart is influenced by the size and the occupation of the +individual being larger in the large individual than in the small, and +larger in the active and vigorous than in the inactive. Generally +speaking, the heart is about as large as the closed fist of its +possessor. + +Imperfections of the heart which interfere with its action may be the +result of failure of development or disease. An imperfect heart which +can, however, fully meet the limited demands made upon it in +intra-uterine life, may be incapable of the work placed upon it in +extra-uterine life. Children with imperfectly formed hearts may be +otherwise perfect at birth, but they have a bluish color due to the +imperfect supply of the blood with oxygen, and are known as blue +babies. The condition becomes progressively worse due to the +progressive demands made upon the heart, and death takes place after +some days or months or years, the time depending upon the degree of +the imperfection. + +Much of the damage of the heart in later life is due to infection. The +valves of the heart are a favorite place for attack by certain sorts +of bacteria which get into the blood. This is due to the prominent +position of the valves which brings them in contact with all the blood +in the body, the large extent and unevenness of the surface and to the +rubbing together and contact of their edges when closed. At the site +of infection there is a slight destruction of tissue and on this the +blood clots producing rough wart-like projections. The valves in some +cases are to a greater or less extent destroyed, they may become +greatly thickened and by the deposit of lime salts converted into +hard, stony masses. Essentially two conditions are produced. In one +the thickened, unyielding valves project across the openings they +should guard, and thus by constricting the opening interfere with the +passage of blood either through the heart or from it. In the other the +valves are so damaged that they cannot properly close the orifices +they guard, and on or after the contraction of the cavities there is +back flow or regurgitation of the blood. If, for instance, the orifice +of the heart into the aorta is narrowed, then the left ventricle can +only accomplish its work of projecting into the aorta a given amount +of blood in a given time by contracting with greater force and giving +a greater rapidity to the stream passing through the narrow orifice. +This the heart can do because, like all other organs of the body, it +has a large reserve force which enables it, even suddenly, to meet +demands double the usual, and like all other muscles of the body it +becomes larger and stronger by increased work. The condition here is +much simpler than when the same valve is incapable of perfect closure, +or when both obstruction and imperfect closure, are combined as they +not infrequently are. In such cases the ventricle must do more than in +the first case. It must force through the orifice, which may be +narrowed, the amount of blood which is necessary to keep up the +pressure within the aorta and give to the circulation the necessary +rapidity of flow, and also the amount which flows back into the heart +through the imperfectly acting valve. This it can do by contracting +with greater force upon a larger amount of blood, the cavity becoming +enlarged to receive this. Not only may such damage to the valves be +produced, but the muscular tissue of the heart may suffer from +defective nutrition or from the effect of poisons, whether these are +formed in the body as the effect of disease or introduced from +without; or in consequence of disease in the lungs the flow of blood +through them may be impeded, or disease elsewhere in the body, as in +the kidneys may, by increasing the pressure of the blood within the +arteries, throw more than the usual amount of work upon the heart. + +The power of the heart in meeting these conditions, however various +they are and however variously they act, seems little short of +marvellous, and it goes on throwing three and one-third ounces of +blood seventy or eighty times a minute into a tube against nine feet +of water pressure, working often perfectly under conditions which +would be fatal to a machine. As long as this goes on the injury is +said to be compensated for; the increased work which the heart is able +to accomplish by the exercise of its reserve force and by becoming +larger and stronger enables it to cope with the adverse conditions. +With increased demand for work there is a gradual diminution of the +reserve force. An individual may be able to carry easily forty pounds +up a hill and by exerting all his force may carry eighty pounds, but +if he habitually carries the eighty pounds, even though the muscles +become stronger by exercise the load cannot be again doubled. The +dilatation of the heart which is so important in compensation is +fraught with danger, because any weakening of the muscle increases the +dilatation, until a point is reached when, owing to the dilatation of +the orifices between auricles and ventricles, the valves become +incompetent to close them. + +When the heart is not able to accomplish its work, the effect of the +condition becomes apparent by the accumulation of blood within the +veins and a less active circulation. This affects the nutrition and +the capacity for work of all the organs of the body, and the imperfect +function of the organs may in a variety of ways make still greater +demands upon an already overloaded heart. Other conditions supervene. +The increased pressure within the veins and capillaries due to the +impossibility of the blood in the usual amount passing through or from +the heart increases the amount of fluid in the tissues. There is +always an interchange between the blood within the vessels and the +fluid outside of them; the passage of fluid from the vessels is +facilitated by the increased pressure within them, just as pressure +upon a filtering fluid increases the rapidity of filtration, and the +increase of pressure within veins and capillaries impedes passage of +tissue fluid into them. The fluid accumulates within the tissues +leading to dropsy, or the accumulation may take place in some of the +cavities of the body. The diminished flow of blood through the lungs +prevents its proper oxygenation; this may also be interfered with by +the accumulation of fluid within the air spaces of the lungs. + +Every additional burden thrown upon the heart increases the evil. In +women the additional burden of pregnancy may suffice to overcome a +compensation which has been perfect, and the same may result from an +acute attack of disease. Age, diminishing as it does the capacity for +work in all organs, diminishes the compensation capacity of the heart, +and a heart which at the age of forty acts perfectly may break down at +the age of fifty. Compensation may be gained in other ways, as by +reducing the demand made upon the heart by changing the mode of life, +by leading an inactive rather than an active life, by avoiding +excitement or any condition which entails work of the heart. Social +conditions are of great importance; it makes a great difference +whether the unfortunate possessor of such a heart be a stevedore whose +capital lies in the strength of his muscles, or a more fortunately +placed member of society for whom the stevedore works and whose +occupation or lack of occupation does not interfere with the +adjustment of his external relations to the condition of his heart. + +Disease of the nervous system does not differ from disease elsewhere. +The system is complex in structure and in function. It consists in +nerves which are composed of very fine fibrils distributed in all +parts of the body and serve the purpose of conduction, and a central +body composed of the brain and spinal cord which is largely cellular +in character; it receives impressions by means of the nerves and sends +out impulses which produce or affect action in all parts. By means of +the organs of special sense, the brain receives impressions from the +outer world which it transforms into the concepts of consciousness. +Many of the impressions which the central nervous system receives from +nerves other than those of special sense and even many of the +impressions from these and the impulses which it sends out do not +affect consciousness. The memory faculty is seated in the brain and +all parts of the brain are closely connected by means of small nerve +fibres. The nervous system plays an important part in the internal +regulation and coordination of all parts of the body, and it is by +means of this that the general adjustment of man with his environment +is effected. + +Malformations of the brain, except very gross conditions which are +incompatible with extra-uterine existence, are not very common. At +birth those parts of the brain which are the seat of memory and what +are understood as the higher faculties are very imperfectly developed. +Variations in structure are extremely common, there are differences in +different individuals in the nerves and in the number, size, form and +arrangement of the nerve cells, and so complex is the structure that +considerable variation can exist without detection. The tissue of the +central nervous system has a considerable degree of resistance to the +action of bacteria, but is, however, very susceptible to injury by +means of poisons. Serious injury or destruction of tissue of the brain +and spinal cord is never regenerated or repaired, but adjustment to +such conditions may be effected by reciprocity of function, other +cells taking up the functions of those which were destroyed. + +Certain parts of the brain are associated with definite functions; +thus, there are areas which influence or control speech and motion of +parts as the arm or leg, and there are large areas known as the silent +areas whose function we do not know. All activity of the central +nervous system, however expressed, is due to cell activity and is +associated with consumption of cell material which is renewed in +periods of repose and sleep. Fig. 13 shows a nerve cell of a sparrow +at the end of a day's activity and the same after the repose of a +night. + +Diseases of the nervous system have a special interest in that they so +often interfere with man in his relations with his fellows. In +diseases of other organs the disturbances set up concern the +individual only. Thus, others need not be disturbed save by the +demands made on their sympathies by an individual with a cold in the +head or a cancer of the stomach. Disease of the nervous system is +another affair, instead of those reactions and expressions of activity +to which we are accustomed and to which society is adjusted, the +reactions and activities are unusual and the individual in consequence +does not fit into the social state and is said to be anti-social. +There are all possible grades of this, from mere unpleasantness in the +social relations with such an individual, to states in which he is +dangerous to society and must be isolated from it. Insanity is an +extreme case. There is no disease signified in the expression, but it +is merely a legal term to designate those individuals whose actions +are opposed to the social state and who are not responsible for them. +In insanity there is falsity in impressions, in conceptions, in +judgment, a defective power of will and an uncontrollable violence of +emotion. The individual is prevented from thinking the thoughts or +feeling the feelings and doing the duties of the social body in the +community in which he lives. The insane are out of harmony with their +social environment, but not necessarily in opposition to it. + +There is no very sharp line between insanity and criminality. The +criminal is in direct antagonism to the laws of social life. An insane +person may cause the same injury to society as a criminal, but his +actions are not voluntary, whereas the criminal is one who can control +his actions, but does not. Mentally degenerated persons, however, can +be both insane and criminal. Whatever the state of society, this +reprobates the actions of one opposed to it; in a society in which it +were usual to appropriate the possessions of others or to devour +unpleasant or useless relatives, virtue and lack of appetite would be +reprobated as unsocial. + +The symptoms of insanity or the manner in which the defective action +of the brain expresses itself and the various underlying pathological +changes vary, and by combining these it has been possible to subdivide +insanity into a number of distinct forms. There are both intrinsic and +extrinsic causes of insanity. The intrinsic are the structural +differences in the brain as compared with the normal or usual, whether +these are due to imperfection in development or to defective heredity +or to the injury of disease; the extrinsic causes are those which come +from without and bring the intrinsic into activity. Syphilis is a +frequent cause of insanity, and probably the only cause of the +condition known as general paralysis of the insane, acting by means of +the injury which it produces in the cortex of the brain. The abuse of +alcohol is another fertile cause, but the changes produced in this are +not so obvious as in the case of syphilis. Tumors of the brain are not +infrequently a cause, and the same is true of infections, even those +not located in the brain. How susceptible the brain is to the effects +of the toxines of the infectious diseases is shown in the frequency of +delirium in these diseases. There is an interesting relation between +this and alcoholism. Alcohol abuse may produce injury, but not +sufficient to manifest itself under ordinary conditions; when, +however, the action of toxic substance is superadded to the effect of +the alcohol the delirium of fever is more marked. + +Probably of greater importance than the acquired pathological +conditions of the brain in producing insanity is a congenital +condition in which the nervous system is defective. The most fertile +cause of insanity lies in the inheritance; by this it must not be +understood that insane parents produce insane offsprings, but that +conditions inherited from immediate or remote ancestors appear in a +diminished resistance of the nervous system which is sooner or later +expressed as insanity. Given such a defective nervous system, +extrinsic conditions which would have no effect on another individual +or would be felt in different ways may produce insanity. In these +cases occupation plays a great role. The excitement and privations of +war especially in the tropics and the ennui of camps leads to insanity +in soldiers; occupations such as that of the baker in which there is +loss of sleep and the mental strain of students can all act in the +same way. A woman who gives no sign of nervous defect may become +insane under the strain of pregnancy. + +Although insanity is determined by the social relations of man, that +part of the social organization which is termed _Society_, and +which has been developed by the idle as a diverting game, is a fertile +source of nervous disease and even of insanity, affecting particularly +females. The strenuosity of the life, the nervous excitement +alternating with ennui, the lack and improper times of sleep, the lack +of rest and particularly of restful occupation, the not infrequent use +of alcohol in injurious amounts, are all factors calculated to make a +defect operative. The so-called "coming out" of young girls is an +important element in the game, and their headlong plunge into such a +life at a period under any conditions full of danger to the nervous +system is especially to be reprobated. If we consider the influence of +the game in other respects as conducing to lack of moral sense, to +alcoholic abuse (for without the seeming stimulation, but which is +really the blunting of impressions which alcohol brings, the game +would not be possible), to discontent, to mental enfeeblement, it is +all bad. Curiously enough the game is one which in all periods has +been played by the idle, but its evil influence is greater now than +before when it was the game of royalty chiefly, because there are now +more people living from the work of others. + +The unusual mental action of the insane not infrequently expresses +itself by suicide. The analysis of three hundred deaths from suicide +showed pathological changes in the brain in forty-three per cent, and +when we think that mental disturbances are very often without +recognizable anatomical changes after death, the percentage is very +large. In another analysis of one hundred and twenty-four suicides +forty-four of these were mentally affected to various degrees. Five of +the men and seven women were epileptics, in ten of the families there +was hysteria, twenty-four of the men and four of the women were +chronic alcoholics. + +It is extremely difficult at the present time to say whether insanity +is increasing. Statistics in all lands giving the numbers committed to +insane hospitals show on their face a great increase, but so many +factors enter into these statistics that their value is uncertain. +There is now an ever-increasing provision for the care of the insane. +Owing to the recognition of insanity as a part of nervous disease and +its separation from criminality there is no longer the same attempt to +conceal it as was formerly the case, and hospitals for the insane are +no longer associated with ideas of Bedlam. It is generally believed +that modern conditions in the hurry and excitement of life, and the +extreme social differences, the greater urban life, the greater +extension of factory life, all tend to an increase in insanity, but +there is no absolute proof that this is true. We know very little +about insanity in the Middle Ages, but the conditions then were not +conducive to a quiet life. There prevailed then as now excess and +want, luxury and poverty, enjoyment and deprivations, balls and dinner +parties and other features of the social game. There were factions in +the cities, public executions, not infrequent sieges, scenes of +horror, epidemics, famines, and all these combined with religious +superstition and the often unjust and cruel laws should have been +factors for insanity. There were actual epidemics of insanity +affecting masses of the population, as shown in the children's +crusade, the Jewish massacres and the dancing mania in the Rhine +provinces. Where civilization seems to be the highest, statistics show +the most insane, but this most probably depends upon better +recognition of the condition and better provision for asylum care. + +The so-called functional diseases have a close relation with diseases +of the nervous system, for they chiefly concern the reactions of nerve +tissue. Disease expressing itself in disturbance of function only, +does not seem to fit in with the conceptions of disease which have +been expressed, nor can we imagine a disturbance of function which +does not depend upon a change of material. Living matter does not +differ intrinsically from any other sort of matter; like other matter +its reactions depend upon its composition structure[1] and the +character of the action exerted upon it. By functional disease there +is expressed merely that no anatomical or chemical change is +discoverable in the material which gives the unusual reaction. The +further our researches into the nature of disease extend, particularly +the researches into the physiology and chemistry of disease, the +smaller is the area of functional disease. In functional disease there +may be either vague discomfort or actual pain under conditions when +usually such would not be experienced, and on examination no condition +is found which in the vast majority of cases would alone give rise to +that impression on the nervous system which is interpreted as pain. In +the production of the sensations of disease there can be change at any +place along the line, in the sense organs, in the conducting paths or +in the central organ. Thus there may be false visual impressions which +may be due to changes in the retina or in the optic nerve or in the +brain matter to which the nerve is distributed. It is perfectly +possible that substances of an unusual character or an excess or +deficiency of usual substances in the fluids around brain cells may so +change them that such unusual reactions appear. There may be, of +course, very marked individual susceptibility, which may be congenital +or acquired. The perception of every stimulus involves activity of the +nerve cells, and it is possible that the constant repetition of +stimuli of an ordinary character may produce sufficient change to give +rise to unusual reactions, and this particularly when there is lack of +the restoration which repose and sleep bring. We know into what a +condition one's nervous system may be thrown by the incessant noise +attending the erection of a building in the vicinity of one's house or +the pounding of a plumber working within the house, this being +accentuated in the latter case by the thought of impending financial +disaster. Even the confused and disagreeable sound due to the clatter +of high-pitched women's voices at teas and receptions may, when +frequently repeated, be productive of changes in the nerve cells +sufficiently marked to give rise to the unusual reactions which are +evidence of disease. + +In the condition known as neurasthenia, which is often taken as a type +of a functional disease, the basal and intrinsic cause is activity of +the nervous system with the using up of material which is not +compensated for by the renewal which comes in repose and sleep. +Neurasthenia is one of the common conditions of our civilization, +found among children and adults, the poor and rich, the idle and the +factory worker; it is rife in the scholastic professions and among +those who earn their living by brain work. It seems to be more common +in the upper classes and particularly in the women, but this is +because these are more subject to medical care and the condition is +more in evidence. There are all sorts of symptoms attached to the +condition, for the unusual mental action can be variously expressed. +The cerebral form has been thus described by a well-known medical +writer: "One of the most characteristic features of cerebral +neurasthenia is a weary brain. The sensation is familiar enough to any +fagged man, especially if he fall short of sleep. Impressions seem to +go half into one's head and there sink into a woolly bed and die. +Voices sound far off, the lines of a book run into one another and the +meaning of them passes unperceived. Doors bang and windows rattle as +they never did before; if a shoestring breaks, an imprecation is upon +the lips. Business matters are in a conspiracy to go wrong. Letters +are left unopened partly from want of will, partly from a senseless +dread lest they contain bad news. At night the patient tosses on his +bed possessed by all the cares which blacken with darkness. Headache +is common, loss of memory is distressing, and in severe cases it is +wider and deeper than mere inattention can explain. There is often the +torture of acute hearing, or an inability to suppress attention; the +hater of clocks and crowing cocks is a neurasthenic." The disease is +especially common in the women players of the social game, and its +unhappy victims too often seek relief from the nervous irritability +which is a common early symptom in still greater nervous excitement. +It is a sad commentary on our civilization that one of the means of +treatment for these persons which has been found efficacious is to +supply them with some restful household occupation such as knitting or +plain sewing, and there are institutions which combine refuge from +social activities, often called duties, with simple occupation. + +FOOTNOTE: +[1] By structure as used in this wide sense, there must be +understood not merely the anatomical structure, which is revealed by +the dissecting knife and microscope, but molecular structure, or the +manner in which elements are arranged to form the molecule, as well. + + + + +CHAPTER XII + +THE RAPID DEVELOPMENT OF MEDICINE IN THE LAST FIFTY YEARS.--THE +INFLUENCE OF DARWIN.--PREVENTIVE MEDICINE.--THE DISSEMINATION OF +MEDICAL KNOWLEDGE.--THE DEVELOPMENT OF CONDITIONS IN RECENT YEARS +WHICH ACT AS FACTORS OF DISEASE.--FACTORY LIFE.--URBAN LIFE.--THE +INCREASE OF COMMUNICATION BETWEEN PEOPLES.--THE INTRODUCTION OF PLANT +PARASITES.--THE INCREASE IN ASYLUM LIFE.--INFANT MORTALITY.--WEALTH +AND POVERTY AS FACTORS IN DISEASE. + + +Certain conditions have arisen in the past fifty years which have +profoundly affected the thoughts, the beliefs and the activities of +man. Within this period what is generally known as Darwinism, +including under this evolution, has developed. Unlike theories which +came from philosophical speculation only, the theory of evolution was +one which could be subjected to observation and experiment. It freed +man's mind from dogmas, it stimulated the imagination, it enlarged the +territory in which it seemed possible to extend knowledge by the +methods of science, and has resulted in an enormous increase of +knowledge. This has been more striking in medical science than +elsewhere, and in this of more far-reaching influence. Evolution +coincided with another important development. History shows that all +great periods of civilization have at their back sources of energy. In +the civilizations of the past such sources of energy have come from +the enslavement of conquered peoples or from commerce, or more direct +forms of robbery, which have enabled a favored class to appropriate +for its purposes the results of the work of others. While these +sources have not been absent in the development of our civilization, +the great source of energy has come from the rapid, and usually +wasteful and reckless, utilization of the stored energy of the earth. +The almost incredible advance in medical and other forms of scientific +knowledge and the utilization of this knowledge is largely due to the +greater forces which we have become possessed of. + +Disease plays such a large part in the life of man and is so closely +related to all of his activities that the changes in this period must +have exerted an influence on disease. We have already seen that within +the period we have obtained knowledge of the causes of disease and the +conditions under which these causes became operative. The mystery +which formerly enveloped disease is gone; disease is recognized as due +to conditions which for the most part are within the control of man, +and like gravity and chemical attraction it follows the operation of +definite laws. There has been developed within the period what is +known as preventive medicine, which aims rather at prevention than +cure, and the resources of prevention are capable of much greater +extension. + +Have there been new conditions developed within the period, or an +increase of existing conditions which can be regarded as disease +factors and which counterbalance the results which have come from the +knowledge of prevention and cure? There has been an increase of +certain factors of immense importance in the extension of disease. +These are: + +1. The increase in industrialism, involving as this does an increase +in factory life. In many ways this is a factor in disease. (_a_) By +favoring the extension of infection, particularly in such diseases as +tuberculosis. (_b_) The life indoors, and frequently with the +combination of insufficient air and space, produces a condition of +malnutrition and deficient general resistance. (_c_) The family life +is interfered with by the mothers, whose primary duty is the care of +home and children, working in factories, and the too frequent +conversion of the house into a factory. (_d_) The influence of factory +life is towards a loss of moral stamina rendering more easy of +operation the conditions of alcoholism and general immorality. How +great has been this increase in industrialism, fostered as it has been +by conditions both natural and artificially created by unwise +legislation, is shown in the figures from the last census. The number +of factory operatives increased forty per cent between 1899 and 1909 +and the total population of the country in the period between 1900 and +1910 increased twenty per cent. It is probable that the future will +see an extension rather than a diminution of mass labor. + +2. The increase in urban life is as conspicuous as the increase in +industrialism. In 1880, twenty-nine and five-tenths per cent of the +population was urban and seventy and five-tenths per cent was rural; +in 1910, forty-six and three-tenths per cent was urban and fifty-three +and seven-tenths was rural, the increase being most marked in cities +of over five hundred thousand inhabitants. Of the total increase in +population between 1900 and 1910, seven-tenths per cent was in the +cities and three-tenths per cent in the country. City life in itself +is not necessarily unhealthy and there are many advantages associated +with it. The conditions which have chiefly fostered it are the +immigration of people who are accustomed to community life, the +increase in factory life and the increased number of people of wealth +who seek the advantages which the city gives them. The city has always +been the favored playground for the social game. The unhealthy +conditions of city life are due to the crowding, the more uncertain +means of livelihood, the greater influence of vice and alcoholism. +Prostitution and the sexual diseases are almost the prerogatives of +the cities. + +3. All means of transportation have increased and communication +between peoples has become more extended and more rapid. In the past +isolation was one of the safeguards of the people against disease. +With the increase and greater rapidity of communication there is a +tendency not only to loss of individuality in nations as expressed in +dress, customs, traditions and beliefs, but many diseases are no +longer so strictly local as formerly--pellagra, for example. Only +those diseases which are transmitted by insects which have a strictly +local habitat remain endemic, although the region of endemic +prevalence may become greatly extended, as is seen in the distribution +of sleeping sickness. Diseases of plants and of animals have become +disseminated. Any plants desirable for economic use or for beauty of +foliage and flower become generally distributed, their parasites are +removed from the regions where harmonious parasitic inter-relations +have been established, and in new regions the parasites may not find +the former restrictions to their growth. There have been many examples +of this, such as the ravages of the brown-tail and gypsy moths which +were introduced into New England and of the San Jose scale which was +introduced into California. There have been many other examples of the +almost incredible power of multiplication of an animal or plant when +taken into a new environment, removed from conditions which held it in +check, as the introduction of the mongoose into Jamaica, the rabbit +into Australia, the thistle into New South Wales and the water-plant +chara into England. + +It is very difficult to say, but it seems as though there is an +increasing unevenness in the distribution of wealth, an increase in +the number of persons who live at the expense of the laboring class. +Mass labor, effective though it be, makes it easier to divert the +proceeds of labor from the laborers. The evidence of this is seen in +the increase in number and the prosperity of those pursuits which +purvey to luxury, as the automobile industry and the florists' trade +and the greatly increased scope and activity of the social game. On +the other hand, there is an increase in the number of people who are +to a greater or less extent dependent upon extraneous aid, evinced +among other ways by the increase in the asylum populations. Both these +conditions, wealth and poverty, are important disease factors. +Tuberculosis is now a disease of the proletariat chiefly. The measures +both of prevention and cure can be and are carried out by the +well-to-do, but the disease must remain where there are the conditions +of the slums. Of all the conditions favoring infant mortality poverty +comes first. In Erfurt, a small city of Germany, of one thousand +infants born in each of the different classes, there died of the +illegitimate children three hundren and fifty-two; of those of the +laboring class, three hundred and five; of those in the medium station +(official class largely), one hundred and seventy-three; of those in +higher station, eighty-nine. The same relation of infant mortality to +poverty becomes apparent when estimated in other ways. In Berlin, with +an average infant mortality of one hundred and ninety-six per +thousand, the deaths in the best districts of the city were fifty-two +and in the poorer quarters four hundred and twenty. The effect of +poverty is seen particularly in the bottle-fed infants; with natural +nursing the child of poverty has almost as good a chance as the child +of wealth. From reasons which are almost self-evident, the mortality +in illegitimate infants is almost double that of the legitimate. The +greater infant mortality in poverty is due to the more numerous +children preventing individual care, the separation of the mother from +the nursing child in consequence of the demand made upon her earning +capacity, and the decline in breast nursing. Wealth is on the whole +more advantageous from the narrow point of view of disease than is +poverty, but if we regard its influence on the race its advantages are +not so evident. Nothing can be worse for a race than that it should +die out, and wealthy families have never reproduced themselves. +Conditions always tending to destruction are a necessary part of the +environment of poverty; wealth voluntarily creates these conditions, +and chiefly by the pernicious influence of its amusements on the +young. + +A new and in many respects a nobler conception of medicine has been +developed. Formerly medical practice was almost exclusively a personal +service to the sick individual, and measures looking toward the +general relief of disease and its prevention received scanty +consideration. The idea of a wider service to the city, to the state, +to the nation, to humanity rather than the personal service to the +individual, is becoming dominant in medicine. This is seen in the +establishment of laboratories by boards of health in cities and states +in which knowledge obtained by exact investigations can be made of +direct service to the people; in the medical inspection of schools and +factories; in promulgating laws directed against conditions which +affect health, in the extension of hospitals, and in divers other +ways. The idea of public service and of returning to the people in an +effective way some of the results of their labor also underlies the +large donations which have been given for the creation of special +laboratories and institutes in which, through research, greater +knowledge of disease may be obtained and made available. The +researches which have been made on the nutrition of man and the +nutritive value of different foods are of great importance, and this +knowledge has not yet begun to be applied as it should be. + +There seems to be a balance maintained between the restriction of +disease by prevention and the increased influence of social conditions +which are in themselves factors of disease. Preventive medicine seems +to have made possible, by restricting their harmful influence, the +increase in industrialism, in urban life, and in the +intercommunications of peoples. The most important aid in the future +to the influence of preventive medicine must be the education of the +people so that the conditions of disease, the intrinsic and the +extrinsic causes and the manner in which these act, shall all become a +part of general knowledge, and the sympathy of the people with health +legislation and their active assistance in carrying out measures of +prevention may be obtained. The effect of social conditions on disease +must become more generally recognized. + + + + +GLOSSARY + + +ATROPHY--A condition of imperfect nutrition producing diminution in +size and loss of function of parts. + +BERTILLON--A French anthropologist who devised a system of +measurements of the human body for purposes of identification. + +BLOOD-PLASMA--The fluid of the blood. + +CELL--The unit of living matter. Living things may be unicellular or +composed of a multitude of cells which are interdependent. The +general mass of material forming the cell is termed cytoplasm. In this +there is a differentiated area termed nucleus which governs the +multiplication of cells. In the nucleus is a material termed chromatin +which bears the factors of heredity. + +CHEMOTROPISM--The influence of chemical substances in directing the +movement of organisms. + +EXUDATE--The material which passes from the blood into an injured part +and causes the swelling. + +FIBRIN--The gelatinous material formed in the blood when it clots. + +HAEMOGLOBIN--A substance which gives the red color to the blood; by +means of its ready combination with the oxygen of the air in the lungs +this necessary element is carried to all parts of the body. + +INFLAMMATION--Literally a "burning"; the changes which take place in a +part after injury. + +LYMPH--The fluid which is contained in the lymphatic vessels--nodes. +Circumscribed masses of cells connected with the lymphatic vessels. + +OSMOSIS--The process of diffusion between fluids of different +molecular pressures. + +SPORE FORMATION--A mode of reproduction in lower forms of life by +which resistant bodies, _spores_, are formed. These have many +analogies with the seed of higher plants. + +SYMBIOSIS--A mutual adaptation between parasite and host. + +TRANSUDATION--The normal interchange of fluid between the blood and +the tissue fluids. The material interchanged is the transudate. + +TROPISM--The influence of forces which direct the movement of cells. + +ULTRA-MICROSCOPE--A form of microscope which by means of oblique +illumination renders visible objects so small as to be invisible with +the ordinary microscope. + +VIRUS--A substance either living or formed by living things which may +cause disease. + + + + +INDEX + + +Amoeba, 13 + +Anthrax, 109 + +Antitoxin, 154 + + +Bacteria, 116 + adaptation in, 123 + aerobic, 122 + anaerobic, 122 + artificial cultivation of, 119 + distribution in nature, 121 + growth and reproduction, 118 + mode of action in disease, 144 + size, 117 + spore formation, 118 + substances affecting growth of, 123 + toxin production by, 144 + variations in, 123 + +Blood, 35 + circulation of, 33, 80 + vessels, 32 + +Body, 22 + defenses of, 146 + organs of, 28 + reserve force of, 50 + surfaces of, 22 + +Brain, 31 + + +Cerebro-spinal meningitis, 188 + +Chemotropism, 93 + +Cretinism, 37 + + +Darwinism, 240 + +Death, 57 + decomposition after, 51 + rigor after, 60 + signs of, 59 + +Disease, 1 + action of poisons, 44 + acute and chronic, 219 + industrialism as factor in, 243 + lesions of, 46 + superstitions concerning, 10 + urban life as factor in, 244 + wealth and poverty as factors in, 246 + +Ductless glands, 37 + + +Embryo, 77 + +Epilepsy, 209 + +Eugenics, 215 + + +Foetus, 32 + infection of, 200 + +Foot and Mouth Disease, 129 + +Glands, 22 + +Growth, 62 + + +Heart, 33, 221 + disease of, 223 + +Heliotropism, 93 + +Heredity, 197 + influence of alcohol, 206 + of insanity, 209 + variations and imitations, 204 + +Hookworm disease, 179 + + +Immunity, 148 + theories of, 149 + natural, 150 + +Infection, 135 + from external surface, 136 + from genito-urinary surface, 137 + from lungs, 138 + from mouth, 138 + from stomach and intestines, 139 + from wounds, 141 + in children, 195 + in wild animals, 191 + latent, 166 + mixed, 160 + racial susceptibility to, 191 + resistance to, 143 + by air, 170 + by insects, 171 + +Infectious diseases, 97 + carriers of, 185 + comparison with fermentation, 108 + epidemics of, 98 + endemic, epidemic and sporadic forms, 188 + modes of transmission, 161 + +Inflammation, 80 + acute and chronic, 95 + +Injury, 54-74 + +Insanity, 231 + causes of, 232 + question of increase, 235 + + +Lesion, 17 + +Leucocytes, 36 + migration of, 92 + +Living matter, 10 + + +Malaria, 175 + role of mosquito in transmitting, 178 + +Malformations, 211 + heredity of, 215 + +Maternal impressions, 212 + + +Nervous system, 228 + disease of, 230 + effect of social life on, 233 + +Neurasthenia, 238 + + +Old age, 51 + atrophy in, 51 + blood vessels in, 54 + causes of death in, 56 + in animals and plants, 55 + mental activity in, 53 + +Osmosis, 91 + +Opsonius, 153 + +Ovum, 201 + fertilization of, 198 + infection of, 199 + + +Phagocytosis, 86 + +Plague, 182 + transmission by animals, 183 + +Plasmodium Malariae, 175 + +Preventive medicine, 242 + +Protozoa, 124 + distribution in nature, 125 + mode of growth, 125 + sexual differentiation, 125 + spore formation, 125 + +Polyomyelitis, 190 + + +Repair, 46 + conditions influencing, 47 + + +Scar, 49 + +Skin, 21 + +Sleeping sickness, 173 + +Smallpox, 187 + +Spontaneous generation, 106 + +Sunburn, 83 + +Syphilis, 193 + + +Tetanus, 142 + +Thymus, 52 + +Thyroid, 37 + +Tonsils, 52 + +Toxins, 144 + +Tropisms, 93 + +Trypanosomes, 172 + +Tuberculosis, 163 + infection by sputum, 169 + modes of extension, 163 + +Tumors, 64 + benign and malignant, 69 + cells of, 66 + color, size and shape, 65 + growth of, 65 + importance of, 77 + origin of, 66 + question of increase, 69 + theories of cause, 71 + treatment of, 77 + +Typhoid fever, 170 + + +Ultra-microscopic organisms, 128 + + +Virus, 128 + + +Yellow fever, 178 + + + +***END OF THE PROJECT GUTENBERG EBOOK DISEASE AND ITS CAUSES*** + + +******* This file should be named 15283.txt or 15283.zip ******* + + +This and all associated files of various formats will be found in: +https://www.gutenberg.org/dirs/1/5/2/8/15283 + + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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