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diff --git a/2938.txt b/2938.txt new file mode 100644 index 0000000..5d1fc63 --- /dev/null +++ b/2938.txt @@ -0,0 +1,948 @@ +The Project Gutenberg EBook of Yeast, by Thomas H. Huxley + +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: Yeast + +Author: Thomas H. Huxley + +Posting Date: January 6, 2009 [EBook #2938] +Release Date: November, 2001 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK YEAST *** + + + + +Produced by Amy E. Zelmer + + + + + +YEAST + +By Thomas H. Huxley + + + +I HAVE selected to-night the particular subject of Yeast for two +reasons--or, rather, I should say for three. In the first place, because +it is one of the simplest and the most familiar objects with which we +are acquainted. In the second place, because the facts and phenomena +which I have to describe are so simple that it is possible to put them +before you without the help of any of those pictures or diagrams which +are needed when matters are more complicated, and which, if I had to +refer to them here, would involve the necessity of my turning away from +you now and then, and thereby increasing very largely my difficulty +(already sufficiently great) in making myself heard. And thirdly, I have +chosen this subject because I know of no familiar substance forming part +of our every-day knowledge and experience, the examination of which, +with a little care, tends to open up such very considerable issues as +does this substance--yeast. + +In the first place, I should like to call your attention to a fact with +which the whole of you are, to begin with, perfectly acquainted, I mean +the fact that any liquid containing sugar, any liquid which is formed by +pressing out the succulent parts of the fruits of plants, or a mixture +of honey and water, if left to itself for a short time, begins to +undergo a peculiar change. No matter how clear it might be at starting, +yet after a few hours, or at most a few days, if the temperature is +high, this liquid begins to be turbid, and by-and-by bubbles make their +appearance in it, and a sort of dirty-looking yellowish foam or scum +collects at the surface; while at the same time, by degrees, a similar +kind of matter, which we call the "lees," sinks to the bottom. + +The quantity of this dirty-looking stuff, that we call the scum and the +lees, goes on increasing until it reaches a certain amount, and then +it stops; and by the time it stops, you find the liquid in which this +matter has been formed has become altered in its quality. To begin with +it was a mere sweetish substance, having the flavour of whatever might +be the plant from which it was expressed, or having merely the taste and +the absence of smell of a solution of sugar; but by the time that this +change that I have been briefly describing to you is accomplished the +liquid has become completely altered, it has acquired a peculiar smell, +and, what is still more remarkable, it has gained the property of +intoxicating the person who drinks it. Nothing can be more innocent than +a solution of sugar; nothing can be less innocent, if taken in excess, +as you all know, than those fermented matters which are produced +from sugar. Well, again, if you notice that bubbling, or, as it were, +seething of the liquid, which has accompanied the whole of this process, +you will find that it is produced by the evolution of little bubbles of +air-like substance out of the liquid; and I dare say you all know this +air-like substance is not like common air; it is not a substance which +a man can breathe with impunity. You often hear of accidents which take +place in brewers' vats when men go in carelessly, and get suffocated +there without knowing that there was anything evil awaiting them. And if +you tried the experiment with this liquid I am telling of while it +was fermenting, you would find that any small animal let down into the +vessel would be similarly stifled; and you would discover that a light +lowered down into it would go out. Well, then, lastly, if after this +liquid has been thus altered you expose it to that process which is +called distillation; that is to say, if you put it into a still, and +collect the matters which are sent over, you obtain, when you first heat +it, a clear transparent liquid, which, however, is something totally +different from water; it is much lighter; it has a strong smell, and it +has an acrid taste; and it possesses the same intoxicating power as the +original liquid, but in a much more intense degree. If you put a light +to it, it burns with a bright flame, and it is that substance which we +know as spirits of wine. + +Now these facts which I have just put before you--all but the last--have +been known from extremely remote antiquity. It is, I hope one of the +best evidences of the antiquity of the human race, that among the +earliest records of all kinds of men, you find a time recorded when they +got drunk. We may hope that that must have been a very late period in +their history. Not only have we the record of what happened to Noah, but +if we turn to the traditions of a different people, those forefathers +of ours who lived in the high lands of Northern India, we find that they +were not less addicted to intoxicating liquids; and I have no doubt +that the knowledge of this process extends far beyond the limits of +historically recorded time. And it is a very curious thing to observe +that all the names we have of this process, and all that belongs to +it, are names that have their roots not in our present language, but in +those older languages which go back to the times at which this country +was peopled. That word "fermentation" for example, which is the title +we apply to the whole process, is a Latin term; and a term which is +evidently based upon the fact of the effervescence of the liquid. Then +the French, who are very fond of calling themselves a Latin race, have a +particular word for ferment, which is 'levure'. And, in the same way, we +have the word "leaven," those two words having reference to the heaving +up, or to the raising of the substance which is fermented. Now those are +words which we get from what I may call the Latin side of our parentage; +but if we turn to the Saxon side, there are a number of names connected +with this process of fermentation. For example, the Germans call +fermentation--and the old Germans did so--"gahren;" and they call +anything which is used as a ferment by such names, such as "gheist" and +"geest," and finally in low German, "yest"; and that word you know is +the word our Saxon forefathers used, and is almost the same as the word +which is commonly employed in this country to denote the common ferment +of which I have been speaking. So they have another name, the word +"hefe," which is derived from their verb "heben," which signifies to +raise up; and they have yet a third name, which is also one common in +this country (I do not know whether it is common in Lancashire, but it +is certainly very common in the Midland countries), the word "barm," +which is derived from a root which signifies to raise or to bear up. +Barm is a something borne up; and thus there is much more real relation +than is commonly supposed by those who make puns, between the beer which +a man takes down his throat and the bier upon which that process, if +carried to excess, generally lands him, for they are both derived +from the root signifying bearing up; the one thing is borne upon men's +shoulders, and the other is the fermented liquid which was borne up by +the fermentation taking place in itself. + +Again, I spoke of the produce of fermentation as "spirit of wine." Now +what a very curious phrase that is, if you come to think of it. The old +alchemists talked of the finest essence of anything as if it had the +same sort of relation to the thing itself as a man's spirit is supposed +to have to his body; and so they spoke of this fine essence of the +fermented liquid as being the spirit of the liquid. Thus came about +that extraordinary ambiguity of language, in virtue of which you apply +precisely the same substantive name to the soul of man and to a glass +of gin! And then there is still yet one other most curious piece of +nomenclature connected with this matter, and that is the word "alcohol" +itself, which is now so familiar to everybody. Alcohol originally meant +a very fine powder. The women of the Arabs and other Eastern people are +in the habit of tinging their eyelashes with a very fine black powder +which is made of antimony, and they call that "kohol;" and the "al" is +simply the article put in front of it, so as to say "the kohol." And +up to the 17th century in this country the word alcohol was employed to +signify any very fine powder; you find it in Robert Boyle's works that +he uses "alcohol" for a very fine subtle powder. But then this name of +anything very fine and very subtle came to be specially connected with +the fine and subtle spirit obtained from the fermentation of sugar; and +I believe that the first person who fairly fixed it as the proper name +of what we now commonly call spirits of wine, was the great French +chemist Lavoisier, so comparatively recent is the use of the word +alcohol in this specialised sense. + +So much by way of general introduction to the subject on which I have to +speak to-night. What I have hitherto stated is simply what we may call +common knowledge, which everybody may acquaint himself with. And +you know that what we call scientific knowledge is not any kind +of conjuration, as people sometimes suppose, but it is simply the +application of the same principles of common sense that we apply to +common knowledge, carried out, if I may so speak, to knowledge which is +uncommon. And all that we know now of this substance, yeast, and all the +very strange issues to which that knowledge has led us, have simply come +out of the inveterate habit, and a very fortunate habit for the human +race it is, which scientific men have of not being content until they +have routed out all the different chains and connections of apparently +simple phenomena, until they have taken them to pieces and understood +the conditions upon which they depend. I will try to point out to you +now what has happened in consequence of endeavouring to apply this +process of "analysis," as we call it, this teazing out of an apparently +simple fact into all the little facts of which it is made up, to the +ascertained facts relating to the barm or the yeast; secondly, what has +come of the attempt to ascertain distinctly what is the nature of the +products which are produced by fermentation; then what has come of the +attempt to understand the relation between the yeast and the products; +and lastly, what very curious side issues if I may so call them--have +branched out in the course of this inquiry, which has now occupied +somewhere about two centuries. + +The first thing was to make out precisely and clearly what was the +nature of this substance, this apparently mere scum and mud that we +call yeast. And that was first commenced seriously by a wonderful old +Dutchman of the name of Leeuwenhoek, who lived some two hundred years +ago, and who was the first person to invent thoroughly trustworthy +microscopes of high powers. Now, Leeuwenhoek went to work upon this +yeast mud, and by applying to it high powers of the microscope, he +discovered that it was no mere mud such as you might at first suppose, +but that it was a substance made up of an enormous multitude of minute +grains, each of which had just as definite a form as if it were a grain +of corn, although it was vastly smaller, the largest of these not being +more than the two-thousandth of an inch in diameter; while, as you +know, a grain of corn is a large thing, and the very smallest of +these particles were not more than the seven-thousandth of an inch in +diameter. Leeuwenhoek saw that this muddy stuff was in reality a liquid, +in which there were floating this immense number of definitely shaped +particles, all aggregated in heaps and lumps and some of them separate. +That discovery remained, so to speak, dormant for fully a century, and +then the question was taken up by a French discoverer, who, paying +great attention and having the advantage of better instruments than +Leeuwenhoek had, watched these things and made the astounding discovery +that they were bodies which were constantly being reproduced and +growing; than when one of these rounded bodies was once formed and had +grown to its full size, it immediately began to give off a little bud +from one side, and then that bud grew out until it had attained the +full size of the first, and that, in this way, the yeast particle was +undergoing a process of multiplication by budding, just as effectual and +just as complete as the process of multiplication of a plant by +budding; and thus this Frenchman, Cagniard de la Tour, arrived at +the conclusion--very creditable to his sagacity, and which has been +confirmed by every observation and reasoning since--that this apparently +muddy refuse was neither more nor less than a mass of plants, of minute +living plants, growing and multiplying in the sugary fluid in which the +yeast is formed. And from that time forth we have known this substance +which forms the scum and the lees as the yeast plant; and it has +received a scientific name--which I may use without thinking of it, +and which I will therefore give you--namely, "Torula." Well, this was a +capital discovery. The next thing to do was to make out how this torula +was related to the other plants. I won't weary you with the whole course +of investigation, but I may sum up its results, and they are these--that +the torula is a particular kind of a fungus, a particular state +rather, of a fungus or mould. There are many moulds which under certain +conditions give rise to this torula condition, to a substance which is +not distinguishable from yeast, and which has the same properties as +yeast--that is to say, which is able to decompose sugar in the curious +way that we shall consider by-and-by. So that the yeast plant is a plant +belonging to a group of the Fungi, multiplying and growing and living in +this very remarkable manner in the sugary fluid which is, so to speak, +the nidus or home of the yeast. + +That, in a few words, is, as far as investigation--by the help of one's +eye and by the help of the microscope--has taken us. But now there is an +observer whose methods of observation are more refined than those of men +who use their eye, even though it be aided by the microscope; a man who +sees indirectly further than we can see directly--that is, the chemist; +and the chemist took up this question, and his discovery was not less +remarkable than that of the microscopist. The chemist discovered that +the yeast plant being composed of a sort of bag, like a bladder, inside +which is a peculiar soft, semifluid material--the chemist found that +this outer bladder has the same composition as the substance of wood, +that material which is called "cellulose," and which consists of the +elements carbon and hydrogen and oxygen, without any nitrogen. But then +he also found (the first person to discover it was an Italian chemist, +named Fabroni, in the end of the last century) that this inner matter +which was contained in the bag, which constitutes the yeast plant, was a +substance containing the elements carbon and hydrogen and oxygen and +nitrogen; that it was what Fabroni called a vegeto-animal substance, and +that it had the peculiarities of what are commonly called "animal +products." + +This again was an exceedingly remarkable discovery. It lay neglected +for a time, until it was subsequently taken up by the great chemists of +modern times, and they, with their delicate methods of analysis, have +finally decided that, in all essential respects, the substance which +forms the chief part of the contents of the yeast plant is identical +with the material which forms the chief part of our own muscles, which +forms the chief part of our own blood, which forms the chief part of +the white of the egg; that, in fact, although this little organism is +a plant, and nothing but a plant, yet that its active living contents +contain a substance which is called "protein," which is of the same +nature as the substance which forms the foundation of every animal +organism whatever. + +Now we come next to the question of the analysis of the products, of +that which is produced during the process of fermentation. So far back +as the beginning of the 16th century, in the times of transition between +the old alchemy and the modern chemistry, there was a remarkable man, +Von Helmont, a Dutchman, who saw the difference between the air which +comes out of a vat where something is fermenting and common air. He was +the man who invented the term "gas," and he called this kind of gas "gas +silvestre"--so to speak gas that is wild, and lives in out of the way +places--having in his mind the identity of this particular kind of air +with that which is found in some caves and cellars. Then, the gradual +process of investigation going on, it was discovered that this +substance, then called "fixed air," was a poisonous gas, and it was +finally identified with that kind of gas which is obtained by burning +charcoal in the air, which is called "carbonic acid." Then the +substance alcohol was subjected to examination, and it was found to be +a combination of carbon, and hydrogen, and oxygen. Then the sugar which +was contained in the fermenting liquid was examined and that was found +to contain the three elements carbon, hydrogen, and oxygen. So that +it was clear there were in sugar the fundamental elements which are +contained in the carbonic acid, and in the alcohol. And then came that +great chemist Lavoisier, and he examined into the subject carefully, +and possessed with that brilliant thought of his which happens to be +propounded exactly apropos to this matter of fermentation--that no +matter is ever lost, but that matter only changes its form and changes +its combinations--he endeavoured to make out what became of the sugar +which was subjected to fermentation. He thought he discovered that the +whole weight of the sugar was represented by the carbonic acid produced; +that in other words, supposing this tumbler to represent the sugar, that +the action of fermentation was as it were the splitting of it, the one +half going away in the shape of carbonic acid, and the other half going +away in the shape of alcohol. Subsequent inquiry, careful research with +the refinements of modern chemistry, have been applied to this problem, +and they have shown that Lavoisier was not quite correct; that what he +says is quite true for about 95 per cent. of the sugar, but that the +other 5 per cent., or nearly so, is converted into two other things; +one of them, matter which is called succinic acid, and the other +matter which is called glycerine, which you all know now as one of the +commonest of household matters. It may be that we have not got to the +end of this refined analysis yet, but at any rate, I suppose I may +say--and I speak with some little hesitation for fear my friend +Professor Roscoe here may pick me up for trespassing upon his +province--but I believe I may say that now we can account for 99 per +cent. at least of the sugar, and that 99 per cent. is split up into +these four things, carbonic acid, alcohol, succinic acid, and glycerine. +So that it may be that none of the sugar whatever disappears, and +that only its parts, so to speak, are re-arranged, and if any of it +disappears, certainly it is a very small portion. + +Now these are the facts of the case. There is the fact of the growth of +the yeast plant; and there is the fact of the splitting up of the sugar. +What relation have these two facts to one another? + +For a very long time that was a great matter of dispute. The early +French observers, to do them justice, discerned the real state of the +case, namely, that there was a very close connection between the actual +life of the yeast plant and this operation of the splitting up of the +sugar; and that one was in some way or other connected with the other. +All investigation subsequently has confirmed this original idea. It has +been shown that if you take any measures by which other plants of like +kind to the torula would be killed, and by which the yeast plant is +killed, then the yeast loses its efficiency. But a capital experiment +upon this subject was made by a very distinguished man, Helmholz, who +performed an experiment of this kind. He had two vessels--one of them we +will suppose full of yeast, but over the bottom of it, as this might be, +was tied a thin film of bladder; consequently, through that thin film of +bladder all the liquid parts of the yeast would go, but the solid parts +would be stopped behind; the torula would be stopped, the liquid parts +of the yeast would go. And then he took another vessel containing a +fermentable solution of sugar, and he put one inside the other; and in +this way you see the fluid parts of the yeast were able to pass through +with the utmost ease into the sugar, but the solid parts could not get +through at all. And he judged thus: if the fluid parts are those which +excite fermentation, then, inasmuch as these are stopped, the sugar will +not ferment; and the sugar did not ferment, showing quite clearly, +that an immediate contact with the solid, living torula was absolutely +necessary to excite this process of splitting up of the sugar. This +experiment was quite conclusive as to this particular point, and has had +very great fruits in other directions. + +Well, then, the yeast plant being essential to the production of +fermentation, where does the yeast plant come from? Here, again, was +another great problem opened up, for, as I said at starting, you have, +under ordinary circumstances in warm weather, merely to expose some +fluid containing a solution of sugar, or any form of syrup or vegetable +juice to the air, in order, after a comparatively short time, to see all +these phenomena of fermentation. Of course the first obvious suggestion +is, that the torula has been generated within the fluid. In fact, it +seems at first quite absurd to entertain any other conviction; but that +belief would most assuredly be an erroneous one. + +Towards the beginning of this century, in the vigorous times of the old +French wars, there was a Monsieur Appert, who had his attention directed +to the preservation of things that ordinarily perish, such as meats and +vegetables, and in fact he laid the foundation of our modern method of +preserving meats; and he found that if he boiled any of these substances +and then tied them so as to exclude the air, that they would be +preserved for any time. He tried these experiments, particularly with +the must of wine and with the wort of beer; and he found that if the +wort of beer had been carefully boiled and was stopped in such a way +that the air could not get at it, it would never ferment. What was the +reason of this? That, again, became the subject of a long string of +experiments, with this ultimate result, that if you take precautions to +prevent any solid matters from getting into the must of wine or the wort +of beer, under these circumstances--that is to say, if the fluid has +been boiled and placed in a bottle, and if you stuff the neck of the +bottle full of cotton wool, which allows the air to go through and stops +anything of a solid character however fine, then you may let it be for +ten years and it will not ferment. But if you take that plug out and +give the air free access, then, sooner or later fermentation will set +up. And there is no doubt whatever that fermentation is excited only by +the presence of some torula or other, and that that torula proceeds in +our present experience, from pre-existing torulae. These little bodies +are excessively light. You can easily imagine what must be the weight of +little particles, but slightly heavier than water, and not more than the +two-thousandth or perhaps seven-thousandth of an inch in diameter. They +are capable of floating about and dancing like motes in the sunbeam; +they are carried about by all sorts of currents of air; the great +majority of them perish; but one or two, which may chance to enter into +a sugary solution, immediately enter into active life, find there the +conditions of their nourishment, increase and multiply, and may give +rise to any quantity whatever of this substance yeast. And, whatever +may be true or not be true about this "spontaneous generation," as it +is called in regard to all other kinds of living things, it is perfectly +certain, as regards yeast, that it always owes its origin to this +process of transportation or inoculation, if you like so to call it, +from some other living yeast organism; and so far as yeast is concerned, +the doctrine of spontaneous generation is absolutely out of court. +And not only so, but the yeast must be alive in order to exert these +peculiar properties. If it be crushed, if it be heated so far that its +life is destroyed, that peculiar power of fermentation is not excited. +Thus we have come to this conclusion, as the result of our inquiry, that +the fermentation of sugar, the splitting of the sugar into alcohol and +carbonic acid, glycerine, and succinic acid, is the result of nothing +but the vital activity of this little fungus, the torula. + +And now comes the further exceedingly difficult inquiry--how is it +that this plant, the torula, produces this singular operation of the +splitting up of the sugar? Fabroni, to whom I referred some time ago, +imagined that the effervescence of fermentation was produced in just the +same way as the effervescence of a sedlitz powder, that the yeast was a +kind of acid, and that the sugar was a combination of carbonic acid and +some base to form the alcohol, and that the yeast combined with +this substance, and set free the carbonic acid; just as when you add +carbonate of soda to acid you turn out the carbonic acid. But of course +the discovery of Lavoisier that the carbonic acid and the alcohol taken +together are very nearly equal in weight to the sugar, completely upset +this hypothesis. Another view was therefore taken by the French chemist, +Thenard, and it is still held by a very eminent chemist, M. Pasteur, and +their view is this, that the yeast, so to speak, eats a little of the +sugar, turns a little of it to its own purposes, and by so doing gives +such a shape to the sugar that the rest of it breaks up into carbonic +acid and alcohol. + +Well, then, there is a third hypothesis, which is maintained by another +very distinguished chemist, Liebig, which denies either of the other +two, and which declares that the particles of the sugar are, as it were, +shaken asunder by the forces at work in the yeast plant. Now I am not +going to take you into these refinements of chemical theory, I cannot +for a moment pretend to do so, but I may put the case before you by an +analogy. Suppose you compare the sugar to a card house, and suppose you +compare the yeast to a child coming near the card house, then Fabroni's +hypothesis was that the child took half the cards away; Thenard's and +Pasteur's hypothesis is that the child pulls out the bottom card and +thus makes it tumble to pieces; and Liebig's hypothesis is that the +child comes by and shakes the table and tumbles the house down. I +appeal to my friend here (Professor Roscoe) whether that is not a fair +statement of the case. + +Having thus, as far as I can, discussed the general state of the +question, it remains only that I should speak of some of those +collateral results which have come in a very remarkable way out of the +investigation of yeast. I told you that it was very early observed that +the yeast plant consisted of a bag made up of the same material as that +which composes wood, and of an interior semifluid mass which contains +a substance, identical in its composition, in a broad sense, with +that which constitutes the flesh of animals. Subsequently, after +the structure of the yeast plant had been carefully observed, it was +discovered that all plants, high and low, are made up of separate +bags or "cells," as they are called; these bags or cells having the +composition of the pure matter of wood; having the same composition, +broadly speaking, as the sac of the yeast plant, and having in their +interior a more or less fluid substance containing a matter of the same +nature as the protein substance of the yeast plant. And therefore this +remarkable result came out--that however much a plant may differ from +an animal, yet that the essential constituent of the contents of these +various cells or sacs of which the plant is made up, the nitrogenous +protein matter, is the same in the animal as in the plant. And not only +was this gradually discovered, but it was found that these semifluid +contents of the plant cell had, in many cases, a remarkable power of +contractility quite like that of the substance of animals. And about +24 or 25 years ago, namely, about the year 1846, to the best of my +recollection, a very eminent German botanist, Hugo Von Mohl, conferred +upon this substance which is found in the interior of the plant cell, +and which is identical with the matter found in the inside of the yeast +cell, and which again contains an animal substance similar to that of +which we ourselves are made up--he conferred upon this that title of +"protoplasm," which has brought other people a great deal of trouble +since! I beg particularly to say that, because I find many people +suppose that I was the inventor of that term, whereas it has been in +existence for at least twenty-five years. And then other observers, +taking the question up, came to this astonishing conclusion (working +from this basis of the yeast), that the differences between animals and +plants are not so much in the fundamental substances which compose them, +not in the protoplasm, but in the manner in which the cells of which +their bodies are built up have become modified. There is a sense in +which it is true--and the analogy was pointed out very many years ago by +some French botanists and chemists--there is a sense in which it is +true that every plant is substantially an enormous aggregation of +bodies similar to yeast cells, each having to a certain extent its own +independent life. And there is a sense in which it is also perfectly +true--although it would be impossible for me to give the statement +to you with proper qualifications and limitations on an occasion like +this--but there is also a sense in which it is true that every animal +body is made up of an aggregation of minute particles of protoplasm, +comparable each of them to the individual separate yeast plant. And +those who are acquainted with the history of the wonderful revolution +which has been worked in our whole conception of these matters in the +last thirty years, will bear me out in saying that the first germ of +them, to a very great extent, was made to grow and fructify by the study +of the yeast plant, which presents us with living matter in almost its +simplest condition. + +Then there is yet one last and most important bearing of this yeast +question. There is one direction probably in which the effects of the +careful study of the nature of fermentation will yield results more +practically valuable to mankind than any other. Let me recall to your +minds the fact which I stated at the beginning of this lecture. Suppose +that I had here a solution of pure sugar with a little mineral matter +in it; and suppose it were possible for me to take upon the point of a +needle one single, solitary yeast cell, measuring no more perhaps than +the three-thousandth of an inch in diameter--not bigger than one of +those little coloured specks of matter in my own blood at this moment, +the weight of which it would be difficult to express in the fraction +of a grain--and put it into this solution. From that single one, if the +solution were kept at a fair temperature in a warm summer's day, there +would be generated, in the course of a week, enough torulae to form +a scum at the top and to form lees at the bottom, and to change the +perfectly tasteless and entirely harmless fluid, syrup, into a solution +impregnated with the poisonous gas carbonic acid, impregnated with the +poisonous substance alcohol; and that, in virtue of the changes worked +upon the sugar by the vital activity of these infinitesimally small +plants. Now you see that this is a case of infection. And from the time +that the phenomenon of fermentation were first carefully studied, it +has constantly been suggested to the minds of thoughtful physicians that +there was a something astoundingly similar between this phenomena of +the propagation of fermentation by infection and contagion, and the +phenomena of the propagation of diseases by infection and contagion. +Out of this suggestion has grown that remarkable theory of many diseases +which has been called the "germ theory of disease," the idea, in fact, +that we owe a great many diseases to particles having a certain life of +their own, and which are capable of being transmitted from one living +being to another, exactly as the yeast plant is capable of being +transmitted from one tumbler of saccharine substance to another. And +that is a perfectly tenable hypothesis, one which in the present state +of medicine ought to be absolutely exhausted and shown not to be true, +until we take to others which have less analogy in their favour. And +there are some diseases most assuredly in which it turns out to be +perfectly correct. There are some forms of what are called malignant +carbuncle which have been shown to be actually effected by a sort of +fermentation, if I may use the phrase, by a sort of disturbance and +destruction of the fluids of the animal body, set up by minute organisms +which are the cause of this destruction and of this disturbance; and +only recently the study of the phenomena which accompany vaccination +has thrown an immense light in this direction, tending to show by +experiments of the same general character as that to which I referred as +performed by Helmholz, that there is a most astonishing analogy between +the contagion of that healing disease and the contagion of destructive +diseases. For it has been made out quite clearly, by investigations +carried on in France and in this country, that the only part of the +vaccine matter which is contagious, which is capable of carrying on its +influence in the organism of the child who is vaccinated, is the solid +particles and not the fluid. By experiments of the most ingenious kind, +the solid parts have been separated from the fluid parts, and it has +then been discovered that you may vaccinate a child as much as you like +with the fluid parts, but no effect takes place, though an excessively +small portion of the solid particles, the most minute that can be +separated, is amply sufficient to give rise to all the phenomena of +the cow pock, by a process which we can compare to nothing but the +transmission of fermentation from one vessel into another, by the +transport to the one of the torula particles which exist in the other. +And it has been shown to be true of some of the most destructive +diseases which infect animals, such diseases as the sheep pox, such +diseases as that most terrible and destructive disorder of horses, +glanders, that in these, also, the active power is the living solid +particle, and that the inert part is the fluid. However, do not suppose +that I am pushing the analogy too far. I do not mean to say that the +active, solid parts in these diseased matters are of the same nature as +living yeast plants; but, so far as it goes, there is a most surprising +analogy between the two; and the value of the analogy is this, that by +following it out we may some time or other come to understand how these +diseases are propagated, just as we understand, now, about fermentation; +and that, in this way, some of the greatest scourges which afflict the +human race may be, if not prevented, at least largely alleviated. + +This is the conclusion of the statements which I wished to put before +you. You see we have not been able to have any accessories. If you will +come in such numbers to hear a lecture of this kind, all I can say is, +that diagrams cannot be made big enough for you, and that it is not +possible to show any experiments illustrative of a lecture on such a +subject as I have to deal with. Of course my friends the chemists and +physicists are very much better off, because they can not only show you +experiments, but you can smell them and hear them! But in my case such +aids are not attainable, and therefore I have taken a simple subject and +have dealt with it in such a way that I hope you all understand it, +at least so far as I have been able to put it before you in words; and +having once apprehended such of the ideas and simple facts of the case +as it was possible to put before you, you can see for yourselves the +great and wonderful issues of such an apparently homely subject. + + + + + +End of the Project Gutenberg EBook of Yeast, by Thomas H. Huxley + +*** END OF THIS PROJECT GUTENBERG EBOOK YEAST *** + +***** This file should be named 2938.txt or 2938.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/2/9/3/2938/ + +Produced by Amy E. 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