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Huxley + </title> + <style type="text/css" xml:space="preserve"> + + body { margin:5%; background:#faebd0; text-align:justify} + P { text-indent: 1em; margin-top: .25em; margin-bottom: .25em; } + H1,H2,H3,H4,H5,H6 { text-align: center; margin-left: 15%; margin-right: 15%; } + hr { width: 50%; text-align: center;} + .foot { margin-left: 20%; margin-right: 20%; text-align: justify; text-indent: -3em; font-size: 90%; } + blockquote {font-size: 97%; font-style: italic; margin-left: 10%; margin-right: 10%;} + .mynote {background-color: #DDE; color: #000; padding: .5em; margin-left: 10%; margin-right: 10%; font-family: sans-serif; font-size: 95%;} + .toc { margin-left: 10%; margin-bottom: .75em;} + .toc2 { margin-left: 20%;} + div.fig { display:block; margin:0 auto; text-align:center; } + div.middle { margin-left: 20%; margin-right: 20%; text-align: justify; } + .figleft {float: left; margin-left: 0%; margin-right: 1%;} + .figright {float: right; margin-right: 0%; margin-left: 1%;} + .pagenum {display:inline; font-size: 70%; font-style:normal; + margin: 0; padding: 0; position: absolute; right: 1%; + text-align: right;} + pre { font-style: italic; font-size: 90%; margin-left: 10%;} + +</style> + </head> + <body> +<pre xml:space="preserve"> + +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 + +Release Date: January 6, 2009 [EBook #2938] +Last Updated: January 22, 2013 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK YEAST *** + + + + +Produced by Amy E. Zelmer, and David Widger + + + + + + +</pre> + <p> + <br /><br /> + </p> + <h1> + YEAST + </h1> + <p> + <br /> + </p> + <h2> + By Thomas H. Huxley + </h2> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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." + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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? + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + 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. + </p> + <p> + <br /><br /><br /><br /> + </p> +<pre xml:space="preserve"> + + + + + +End of the Project Gutenberg EBook of Yeast, by Thomas H. 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