Popular Science Monthly/Volume 5/September 1874/Ferments, Fermentations, and Life

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585997Popular Science Monthly Volume 5 September 1874 — Ferments, Fermentations, and Life1874Fernand Papillon





UNTIL very lately, all fermentations were supposed to be produced by the spontaneous decomposition of organic matter within a fermentable liquid. It was said that on contact with air this organic matter undergoes a special change which gives it the character of leaven, and this was regarded as an agent having the power of spreading decomposing movement. It is true, brewer's yeast had long been well known; the facts of its cellular composition and its organization were familiar; but no relation was recognized between this organized condition and those phenomena of fermentation produced by yeast in saccharine liquids, such as grape-juice or the wort of ale. In the first few years of this century Turpin, and afterward Cagniard-Latour, attempted in vain to prove that such a relation existed; it was always denied that any thing else could be observed in alcoholic fermentation than an operation resembling all those slow decompositions that were classed among fermentations. We have admitted, in our time, that alcoholic fermentation, instead of being an exception, is on the contrary the very type of the phenomena we are treating of; that the yeast-cells, far from being unimportant, take an essential part in it, and that in all fermentations whatever there occur low organizations, microscopic corpuscles, more or less analogous to those of yeast. At least this is the first result of investigations carried on in the past fifteen years by several men of science, among whom in the first rank M. Pasteur is to be cited.

M. Pasteur began the course of his labors in 1858, by the study of alcoholic fermentation. He placed it beyond a doubt that, in the case of grape-juice or beer-wort, as in that of any other saccharine liquid exposed to the air, the more or less rapid production of alcohol is always connected with the production of a microscopic fungus, consisting of rounded globules, a few thousandths of a millimetre in diameter. These globules, known under the name of brewer's yeast, multiply in the fermenting liquid at the expense of the organic matters it contains, and, by the exchanges of growth they give rise to, produce decomposition of the sugar into alcohol and carbonic, succinic, and glyceric acids. These are the four invariable products of alcoholic fermentation. Sugar is the food of the yeast-fungus; these products are its excretions. The laws of the inner mechanism that elaborates them are yet unknown. But every thing leads us to believe that the yeast-cells secrete a substance more or less resembling those that work out the phenomena of digestion in the higher animals. Alcoholic fermentation would thus be a kind of digestion of sugar within the globule.

M. Dumas, who signalized his entrance upon the career of studies in natural science half a century ago, by memorable discoveries in microscopic physiology, has lately returned to researches of the same kind, precisely, in respect to fermentations. In M. Pasteur's laboratory at the Normal School he has taken up investigations on this subject, the results of which, quite lately published, show that the distinguished savant in question has lost neither his cautious diligence in experimental processes, nor his lucid conception in the grasp of principles. He has attempted among other things to determine the decomposing force, the amount of activity, possessed by each cell of the alcoholic ferment. To ascertain this, he measured the quantity of sugar decomposed in a given time by a fixed weight of yeast, and he found—after first establishing that a cubic millimetre of yeast contains about 2,772,000 cells—that the power of a million of cells represents the force capable of decomposing four grains of sugar in an hour. If we attempted according to this estimate to express in figures the number of cells employed in producing the wine, beer, and cider, consumed every year, as M. Dumas says, even astronomers would shrink from the task.

This active property of decomposing sugar, and forming alcohol in consequence, does not belong to the cells of brewer's yeast exclusively. Several chemical agents possess the same power, and certain vegetable cells also are adapted to use it. When fruits are placed in a medium filled with oxygen, they absorb this gas, and occasion the release of carbonic acid; if, on the contrary, they are left in carbonic acid or any other inert gas, they effect the production of alcohol. The fruits remain firm and hard, without suffering any external change, but the sugar they contain is transformed in part into alcohol. How is this phenomenon to be explained? In common air, the cell of the fruit is fed by oxygen; if this gas is withheld, it is forced to borrow the materials of nutrition from the fluids that moisten it, that is, from the saccharine juice, and then the latter is decomposed. M. Pasteur has noted that a similar alcoholic fermentation takes place in other vegetable organs, in leaves, for instance, and in every case he has proved that the phenomenon is due to the cells of the vegetables alone, and not to yeast-globules. Far from throwing any doubt on the physiological doctrine of fermentation, these singular facts agree in lending it support, by giving it deeper and more general application.

We have seen that the fermentation of sugar yields alcohol. The latter, brought in contact with certain porous substances, as, for instance, platinum sponge, can absorb the oxygen of the air and transform itself, by oxidation, into acetic acid. A phenomenon of this kind occurs in wine when it sours, the alcohol contained in it being changed into acetic acid; only, the agent in the transformation is in this case a microscopic plant, made up of little elongated globules, some thousandths of a millimetre in diameter. These globules, these mycoderms, develop on the surface of wine exposed to the air, and form a scum which plays the part of storing away a certain stock of oxygen, afterward used to produce acetification in the liquid. This scum, which is called mother of vinegar, only acts while in communication with the air. As soon as it is below the surface, it loses its efficacy, and the production of acetic acid is checked. Thus the development of vinegar in the acetic fermentation is reduced to an oxidation of alcohol, in which microscopic cells are the vehicles of the oxygen.

When milk turns and sours, that phenomenon also is due to the formation of an acid—lactic acid. This substance proceeds from the decomposition of sugar contained in the milk, and this decomposition, again, is a fermentation. The microscopic being that effects it assumes several forms; sometimes it is made up of cells presenting much resemblance to the cells of yeast, sometimes it consists of straight and exceedingly fine rods. Milk also contains casein, which is the substance that composes cheese, and, when the fermentation of the sugar in milk is over, that of the casein begins; after lactic acid, butyric acid is produced. Examining with a microscope the casein transforming into butyric acid, we observe in it little rods, two thousandths of a millimetre in diameter, and of a length from two to five times as great; this is the butyric ferment, which, concurrently with other microscopic vegetable growths, determines in various cheeses the slow production of butyric acid and several analogous acids, equally strong in smell. To cite a last illustration, the decomposition of urine, giving rise to an abundant release of ammoniacal gases, is also the result of a fermentation; under the action of cells smaller than those of brewer's yeast, the contained urea changes to carbonate of ammonia, rendering the liquid highly alkaline and strongly odorous. In short, the fermentations we have just described, and many others of the same kind, participate in the nutrition and development of microscopic beings, of an average size not exceeding some thousandths of a millimetre, and presenting the form sometimes of spheroidal or of egg-shaped globules (as mycoderms, torulacea), sometimes of straight, bent, or curving rods (as vibrios and bacteria). These diminutive beings engender the ferment within the fermenting liquid itself, in the degree and rate of their propagation in it.

There is another class of fermentations in which the immediate presence of definitely-shaped corpuscles cannot be traced. Thus diastasic fermentation consists in the transformation of starch into sugar under the action of a formless yellowish matter, called "diastase." Amygdalic fermentation is that in which amygdaline becomes the essence of bitter almonds, by the action of a like ferment, known as "syraptase." The former takes place in the vegetable embryo when the amylaceous matter of the seed is converted into a soluble sugar, which permeates the growing tissues of the plant. The latter occurs when bitter almonds are crushed in water; on contact with the liquid, the mixture of these odorless kernels takes the characteristic smell of the essence of bitter almonds, which results from the fermentation of amygdaline. We regard as fermentations, moreover, a certain number of similar phenomena which can be produced with the implements of a laboratory, and which are constantly taking place in living organisms, of which the cause is a zymotic substance. There exists, for instance, in the saliva a principle called ptyaline, which, like diastase, converts amylaceous matter into sugar. The gastric juice contains another principle, pepsin, which has the effect of liquefying albuminous substances, so that they may be prepared for absorption. The pancreatic fluid contains another principle which acts in a similar way. Digestion is thus reduced to a series of fermentations, as the ancient chemists had rightly conjectured in regard to it. These different phenomena, as well as those in which organisms take part, have the two general characteristics of fermentation; they occur only within certain limits of temperature, and the weight of the fermentable matter is always much greater than that of the ferment which suffices to decompose it.

To conclude, fermentations occasioned in certain media, by the act of development and nutrition of ascertained microscopic animal or vegetable existences, present a group of well-defined characteristics. They follow obediently all the variations that may occur in the physiological activity of the microscopic beings contained in the liquid. This does not go into fermentation all at once; it delays more or less, and molecular movement makes itself perceptible in it by degrees. The phenomenon is one of evolvement. This appears to be the characteristic of alcoholic, lactic, acetic, butyric, glyceric, and putrid fermentations—all of those, in short, which M. Pasteur has studied with so convincing accuracy. Is it the same with the conversion of amylaceous substances into sugar, under the influence of diastase or ptyaline, with the dissolving of proteic substances by pepsin, with the change of amygdaline into the essence of bitter almonds, by contact with synaptase? Evidently not. These phenomena present another aspect; they show no stages of evolvement. Doubtless they require a certain time for their completion; but they take place all at once, and without any relation to the surrounding air.

These differences between the two kinds of fermentation clearly depend on this: that, in the former, the phenomenon is subjected to the conditions and vital progress of those organized corpuscles which elaborate the ferment within the substance of the fermentable liquids, while, in the latter, the phenomenon is brought about by a ferment already formed and prepared. But this latter ferment is no less of organic origin; it, too, arises from living beings, animal or vegetable. Whether it emanates, like diastase, from the young cells of the seed, or results, like pepsin, from work done in the digestive apparatus, it is the labor of life, just as much as if it had been completed by globules of yeast or bundles of bacteria. Thus the efficient sources of all fermentations are the same. All ferments are at bottom alike, whether procured directly for the fermentable liquid by microscopic bodies inhabiting it, or emanating from corpuscles that inhabit elsewhere. The true doctrine of fermentations consists in this point.

Henceforth, then, we may consider ferments as products of a fecundation taking place in cells, as secretions elaborated by those myriads of infinitely little corpuscles, some crowded, squeezed, condensed, into the palpable organs of animals and plants—others free and moving, disseminated, as we shall see, into vast, intangible space. The energy which distinguishes these microscopic animal and vegetable growths also belongs to the microscopic elements making up the living tissues in the higher animals. We must give to this property, hitherto considered as special, the high dignity of a fundamental and universal attribute of organized cells. We must detect, in the most complex conversions and processes of nutrition in superior beings, the same untiring and primitive force that marks the subtile action of invisible and insignificant monads.

No doubt, the corpuscles of different species––to which, in the last analysis, we reduce animals and plants of every kind and degree—are not identical. Each species has its own structure, its specific energy, its mode of nutrition, its fixed secretions—characteristics, moreover, which vary with circumstances and media. Yet we can point out more than one interesting similarity between certain ones of these species, which seem to discharge quite distinct functions, and hold very unlike stations, in the vast harmony of vital monads. The cells of fruits, when placed in certain conditions, behave, as has been seen, like the cells of brewer's yeast; they both decompose sugar and yield alcohol. We may trace resemblances not less close, as M. Blondeau and M. Pasteur have done, between acetic mycoderms and blood-globules. Both alike serve as carriers of oxygen—the first, for the slow combustion of alcohol; the last, for the slow combustion of the albuminoid matters in animal tissues. It is even likely that there is a principle in mycoderms similar to hemoglobine in the blood-globule, and provided with a special affinity for oxygen. However this may be, comparisons of this kind open a new path for physiology. As that science is definitely summed up in the explanation of existences and processes in the microscopic elements of organs, it is plain that nothing can be more useful to it than the study of these one-celled organisms in which the phenomena are extremely simple, and life is reduced, in a manner, to its primitive factors. It becomes more and more evident that progress in the comprehension of the superior animals is bound, with the very closest ties, to advance in the comprehension of the mechanism of nutrition in the rudimentary units of life, in the smallest beings that it is given us to study.


Now, whence come those organized microscopic corpuscles to which, as we have seen, very many of the alterations of organic matter must be attributed? Upon this great problem, opinions at this day are still very contradictory. Neither patient observations, nor minute experiments, nor profound reasonings, have been wanting; yet some still believe that these little bodies grow, by spontaneous generation, within fermentable liquids, while others assert, and profess to have proved, that they come from germs contained in the air. Certainly, the former opinion involves nothing contradictory nor impossible. Those who reject it by begging the question, in the name of some unknown, mystical doctrine of life, do not even deserve to be listened to in the investigation. It might possibly have occurred that organized beings should be produced, complete at all points, in a medium deprived of organization; yet experiment proves that this does not occur. We must, then, accept the other opinion—the panspermist doctrine—that is to say, we must concede that the germs of microscopic animals and vegetables, with which so many fermentations and factions are connected, exist in the air. This is one of the conclusions, and perhaps the most legitimate and most fertile one, of M. Pasteur's striking studies.

He deserves the glory of it precisely because he has not priority in it. In truth, the originator of this idea only had, and could only have, a dim intuition of it. He could measure neither its importance nor its consequences. The importance and the results of a great idea, whatever it may be, only become apparent when, after undergoing a certain evolution, it has gained the precision, certitude, and establishment, that nothing but long experience can confer upon it. A conception must have acquired some age in science to wear a fixed authority, and bestow fame on those who comprehend, and cause to be comprehended, all its grandeur and power. The circulation of the blood had long been seen by glimpses, in the schools of physiology, when Harvey gave it complete and vigorous demonstration. Gravitation had long invited research, and suggested presentiment, before Newton drew its perfect system. So, too, the panspermist theory, neglected and ignored since the time of its earliest authors—among whom Astier, in 1813, deserves particular mention—has only been definitely established in our time, through the experiments made by M. Pasteur. These experiments, repeated and varied in a thousand ways, all refer to the investigation, by comparison of what takes place in the same fermentable liquid, under the different conditions of exposure to common air, filled with dust, and of contact with purified air. For instance, M. Pasteur puts a certain quantity of a liquid, that readily undergoes change, into glass balls through which a current of air may be made to pass. Fermentation and the development of small organisms take place very soon in the balls through which common air circulates; but, if the air, before entering them, passes through a plug of cotton, no change in the liquid is observed. When the volume of air, thus filtered through cotton, is considerable, the plug is so filled with dust as to turn black. Now, this dust, in addition to a quantity of mineral particles, and fluff of many kinds, contains spores and germs of fermenting substance, as is proved by the fact that the smallest quantity of it, sprinkled in pure liquid, will produce fermentation in it. An experiment of another kind is this: M. Pasteur, by an ingenious arrangement, inserts and withdraws from a glass jar, filled with pure air, the juice from the inside of a single grape, so that, during the experiment, the juice communicates neither with the surface of the grape nor with the atmospheric air. The juice, thus obtained, shows no trace of fermentation, remaining unchanged as long as the jar is closed; but, if it is opened, or if its contents are mixed with a few drops of water in which the surface of the grape has been washed, fermentation is set up in it at once. This is because the outside of grapes is always covered with yeast-germs, even when the bunches have been subjected to constant rains. In this case, plainly, fermentation is due to the germs suspended in the air, or deposited on the surface of the grapes and stems. M. Pasteur draws blood from an animal's veins by a similar process, and introduces it into a glass vessel in contact with pure air. The blood continues fresh for years. M. Pasteur asserts and proves by experiment that grape-juice, milk, blood, and all liquids that most readily undergo change in ordinary conditions, are incapable of fermentation in air which is pure, that is to say, deprived of the corpuscles it contained.

M. Pasteur has made still another set of experiments. He has obtained development of fermentation in liquids freed from albuminoid substances. It was supposed, before his researches, that the cells remarked in the fermentation of grape-juice proceed from the conversion of the albuminoid substances which this fluid contains in its natural state. M. Pasteur prepares a solution of sugar, tartrate of ammonia, and some other salts, and sprinkles a few yeast-globules in it. They swell, develop, and propagate in this artificial medium quite as well as in the grape-juice. So it was supposed that in the acid fermentation of milk the ferment is a product of the conversion of casein. M. Pasteur proves that supposition to be unfounded, by artificially producing the lactic ferment in a compounded liquid containing not a trace of casein. These very delicate experiments have not only increased the vogue of the panspermic theory, but they have been of great value also to vegetable physiology.

Many objections have been raised to these theories on the origin of ferments, to which M. Pasteur has almost always replied by unquestionable facts and solid reasonings, though he has sometimes done himself the injustice to be rough and contemptuous in discussion toward his opponents. Truth is strong enough to indulge charity for error. The gravest of these objections, it must be said, have applied to problems which do not concern the very foundation of the dispute between the panspermist system and its opposite. For instance, M. Trécul, the skillful and noted micrographer, M. Béchamp, and others, have proved that M. Pasteur mistakes with regard to the evolutions and transformations undergone by microscopic beings in fermenting media. M. Pasteur has certainly made more than one mistake on this subject, and there probably does exist between certain ferment-corpuscles a closer relationship than is supposed at the laboratory of the Normal School; but that does not in the least alter the fundamental character of the theory. Attention is also called to the fact that corpuscles with a determinate structure can be produced complete, without germs, in some liquids. No doubt this is true, but only on condition that the liquids are living ones. No doubt the cambium of vegetables, the blastema of animals, and generally all protoplasmic fluids, are fertile hatching-fields for the spontaneous development of the cells and fibres of living tissues. It is thus that the first elements of the embryo show themselves in the animal ovule. And in this respect the labors of Robin, Trécul, Onimus, Legros, and a great number of other observers, are decisive; but life is the property of these protoplasms; they depend upon an organized system. In the depths of the organism, and shielded from the air, they toil at the creation of microscopic corpuscles. Place them in contact with purified air, in M. Pasteur's glass globes, and then they would be barren.

The last objection M. Pasteur has to meet is, that, if the germs of all these microscopic vegetable and animal lives are in the atmosphere, they should be discovered and recognized there. But, in examining the dust of the air microscopically, we do not by any means detect all the rudiments of that infinitely minute flora and fauna whose existence is attested by the fermentations and putrefactions of organic matter. M. Pasteur has thus far met this argument only by the evidence of his experiments which prove that, in contact with purified air, neither fermentations nor putrefactions are possible. That is strictly sufficient, but we can go farther. It is by no means a sure conclusion that these germs do not exist, because many of them are invisible under the lens. To begin with, we do note with certainty a certain number of species in atmospheric dust. It is therefore an admissible presumption that, if the remaining ones elude our eyes and our microscopes, that merely proves them to be smaller than the observed ones. But, perhaps, the problem ought to be viewed in a different way. We believe that these visible germs are the exceptions, that is, that they are beings already arrived at a certain degree of development, and that, in reality, all true germs are of dimensions forever beyond the reach of microscopic observation, even conceiving lenses to be immensely more powerful than they now are. The microscope barely brings within our range of vision points that measure at least a ten thousandth part of a millimetre. The primitive germs of life cannot even approach the millionth part of a millimetre. Physics and metaphysics both assure us that we must here give up the hope of measuring and estimating things according to the powers of our limited senses. An effort is needed to pursue with the mind's eye these perpetually-dwindling dimensions, still to go on though the imagination fails in the task, and to realize at last how far removed are the bounds of the microcosm. If the faculty of reaching out beyond the limits of our nature, which is one of the noblest prerogatives of our intelligence, does not desert us, we attain to the idea of the vital monads of Leibnitz, the organic molecules of Buffon, the comprehension of existence for primal organisms diffused throughout the world by myriads of myriads, and the conception of the infinitely minute within the infinitely minute.

Thus, just as the infinite universe through which the spheres roll is filled with invisible particles of a subtile matter to which physicists and astronomers give the name of ether, and which supplies the only key to cosmic phenomena, the finite universe in which organization unfolds itself is thronged with corpuscles no less invisible, forming what the illustrious Ehrenberg calls the milky-way of lower organisms, and no less essential for explanation of the processes of which we have traced the general course. As there is an ether wanting in life, so there is an ether endowed with life—a vital ether. Both are above denial; they surpass our reason, yet reason cannot but demand them. They elude the close grasp of experiment, yet experiment does not permit them to be avoided; they are unseen, and without them there could be nothing seen. The mind clings to them with the stress of all its power to embrace, perhaps because it feels a secret, mysterious affinity with them, perhaps because it is in substance of the same essence with them.


Our atmosphere, then, is the receptacle for myriads of germs of microscopic beings, which play an important part in the organized world. Penetrating agents of decay, baneful toilers for disease, they lie ever in wait for the chance to pierce the internal machinery of animals and plants, and create slight or grave disturbances within it. Life often resists or escapes them, but nothing can contest with them its deserted vesture. The corpse is their natural aliment, and death their chosen laboratory. There these lowest of created things work out their lofty destiny in the eternal drama of renewal of organic existences.

When the thin pellicle covering sweet fruits is torn at any point, an opening is made for atmospheric germs. Fermenting cells pierce the interior of the fruit, and produce within it fermentation of the sugar, that is to say, the formation of a little alcohol; and this in its turn is susceptible of the passage into acetic fermentation, giving the pulp an acid taste. At last the pulp itself is destroyed by various fungous growths. When a fruit decays and takes a more or less unpleasant flavor, this depends on the intervention of ferment-cells of atmospheric origin, and on the production of acid or alcoholic substances. An able micrographist, M. Engel, who has lately studied these phenomena minutely, discovers that the yeast-cells which thus produce alcoholic fermentation in the juices of fruits present some slight differences in various fruits, neither do they have the same morphological character as those of grape-must or beer-wort. Varieties occur in these cases, corresponding to the different media in which the nutrition of the little fungus takes place.

The microscopic fungi of the atmosphere play as interesting a part in the alteration of wines. These grow acid, change, become filmy or oily, or take on besides a decided bitterness. All these sicknesses depend on the development of different little plants recognized and described by M. Pasteur; and this scientist, not stopping at the solution of the nature of these disorders, has sought the means of preventing them. Resting on some former observations by D'Appert, he conceived the idea of subjecting wines to the action of a very high degree of heat, so as to destroy the yeast-germs. There was no possibility of doubt as to the destruction of these germs and the prevention of any further change, but it might well be asked whether the delicacy and bouquet of certain wines would not be endangered by the effects of heating. Long-continued experiments prove not only that heating is an excellent method for preventing sickness in wines, but also that, instead of impairing their exquisite qualities, it ripens and strengthens them. The recorded minutes of tastings officially performed during the past year by several members of the syndical wine commission, at the suggestion of M. Pasteur, contain decisive testimony on this point. Fine Burgundy wines, heated in bottle seven years ago to temperatures varying between 131° and 149°, appeared, at the end of that time, superior to the same wines not so treated. Persons who spoke with some authority, M. Pasteur says, declared that heating would in time deprive the wine of its color. The contrary is the case, when the air is excluded during the process; the color grows livelier by heating. It was said that heating would in time alter the bouquet of fine wines, giving them dryness and too great age. On the contrary, the bouquet seems to be heightened with the lapse of time, more positively than with wines not heated. In the case of chambertin and volnay particularly, the tasters noticed this fact. M. Pasteur was led by these studies to investigate the cause of the aging of wines, and he discovered that the phenomenon was due to slow oxidation. Wine kept in glass tubes completely filled and closely sealed does not age. By increasing and regulating the aeration of wine, and particularly combining it with heating, he succeeded in manufacturing in one month excellent old wine. In short, oxygen and heat, acting on wine in certain proportions, promote instead of hindering the development of those volatile principles to which the liquid owes its perfume and part of its flavor; but this discovery is additional to those sought. What M. Pasteur did chiefly look for and did find, in giving exact and methodical rules for heating wines, is a process, applicable on a great scale, for preventing the diseases from which the common vineyard products so often suffer, and that fortunate application is a result from his researches on fermentation generally. In the same way, in consequence of the examinations he undertook as to the share of microscopic organisms in the diseases of silk-worms, he was led to prescribe a practical way of hindering the development of these organisms, and thus preventing the malady.

When we inject into the subcutaneous cellular tissue of a living animal a putrefied or septic liquid, that is, one containing those threadlike corpuscles known by the name of vibrios and bacteria, it sometimes happens that the animal experiences no inconvenience. Dogs particularly resist with vigor the poisonous influence of such a fluid, but the case is different with other species, and notably with rabbits. The system becomes the seat of grave phenomena, almost always mortal, of which the general group composes the affection known by the term septicæmia. The microscopic organisms in such a case poison the animal, not only by the mere fact of their presence in the blood, but besides and especially because they develop and propagate in it with astonishing rapidity, in the same way that yeast reproduces itself in barley-wort. But the most singular thing in these pathological fermentations is the fact noted some years ago for the first time by MM. Coze and Feltz, and the study of which M. Davaine took up last year. Davaine demonstrates, by experiments made on rabbits and Guinea-pigs, that one drop of blood, from an animal affected with septicæmia, has the power of imparting the infection to another animal inoculated with it; that a drop taken from the second can transmit the disease to a third, and so on. Still more, very wonderfully, the poisoning power of the blood of these animals increases with the degree of advance in the series of inoculations. The culture of the virus heightens its maleficent properties. This gradual increase of the virulent force is such that, if we take a drop of blood from an animal representing the twenty-fifth term in a series of successive inoculations, and so dilute this drop with water that a drop of the dilution corresponds to one trillionth of the original drop, we get a liquid of which the smallest quantity still displays mortal activity. These experiments of M. Davaine, which exhibit the degree of venom as increasing in an inverse ratio to the apparent quantity of the poison, have been repeated and confirmed by several eminent physiologists, among others by M. Bouley, and have produced a sensation which still continues in the schools of physiology and medicine. Apart from the inherent difficulty of forming a notion as to the influence of those infinitesimal doses, they seemed to yield an argument of a kind to support the assertions of homœopathy. If the difficulty is real, though it may be got over, the argument, we take leave to say, is worthless. Let us look at the difficulty first. This drop which is still mortal, though representing only an infinitely small fraction of the original quantity of poisonous matter to which it is distantly related, permits no corpuscle to be detected. That is true, yet it contains the germs of them, and germs such in number, size, and reproductive power, that nothing prevents them from, breeding again indefinitely, in spite of all efforts tried to get rid of them. The discussions that have just occurred in the Academy of Medicine on this grave subject, almost at the same time that the question of ferments was under debate in the Academy of Sciences, leave no doubt as to the reality of this progressive breeding of virulent germs by culture. But is this any argument for the homœopathists? None whatever. They attribute curative effects to extremely small doses of certain inorganic substances most evidently inert, which can in no way reproduce themselves. If the virulent elements occasion disturbances so profound in animal organisms, it is not by reason of their extreme minuteness, but it is because they multiply with prodigious rapidity in the depths of the tissues and humors, where they labor in a manner opposed to the harmonious life of the body.

However this may be, the vibrios and bacteria have an undeniable share in the production of human maladies. They are found in the blood of persons attacked by infectious disorders, and if in many cases their relation to these disorders is only that of concomitants, in others, their relation of causality is very clearly ascertained. Thus M. Davaine's investigations prove that the maladies called carbuncular, so formidable in men and animals, are due to the excessive development of a species of bacteria in the blood. Typhoid fever also seems to acknowledge a cause of the same kind. Rabbits die from inoculation with blood taken from men attacked by this disease. Our knowledge upon this difficult subject, it must be owned, is very little advanced, in spite of the ardent labors devoted to its extension in the past few years. The illusions of the microscope and the exaggerations of a spirit of routine too often impair the value of studies undertaken in this direction. Without going so far as does the opinion of those who attribute all these disorders to microscopic corpuscles, and regard all morbid phenomena as fermentations, it must at any rate be admitted that these corpuscles, diffused throughout the air, take an important place among the eternal enemies of health. At all times surgeons and physicians have recognized the danger from penetration of common air into the interior of the organism, by the way of wounds or otherwise. We now understand the explanation of the danger. It is not the gases of the air that are dangerous; but the proto-organisms contained in that fluid must be charged with the fatal influence it exerts in traumatic cases, and putrid infection has no other origin. Thus the anxiety of practitioners now is to protect wounds from access by the germs in the air, by means either of impermeable coating, or of antiseptic dressings, containing alcohol or phenic acid, or by pneumatic closing up, or by filtration of the air itself through cotton. Under the influence of ideas distinctly introduced into science by the researches we have just reviewed, several practices in surgery have undergone great modifications.

After examining the alterations produced in the living, we have to consider those occasioned by fermentations in the dead. When life has retreated by slow degrees from all the parts of an organized being; when, after all partial deaths have occurred, total death has possessed the depths of the subject, and broken all the springs of its activity, the work of putrefaction begins. Its task is to unmake this body, to destroy its forms, and dissever its materials. The work to be done is to disorganize it, to reduce it into solids, liquids, and gases, fit to go back again into the vast reservoir whence new life is incessantly issuing. This is the task that heat, moisture, air, and germs, will undertake in unison. It is all performed with steady diligence. Nature knows no delays; as soon as the body is cold, the protecting coating that covers all its surface, the epithelium, decays in places, particularly in the moister parts. The agents of disorganization, vibrios and bacteria, or rather the germs of these thread-like corpuscles, penetrate through the skin, wind into the small ducts, invade the whole blood, and by degrees all the organs. Soon they swarm everywhere, almost as numerous as the chemical molecules in the midst of which they stir and circle. The albuminoid matters are decomposed into fetid gases, escaping into the air. The fixed salts, alkaline and earthy-alkaline, slowly release themselves from the organic matters with which they combined to form the tissues. The fats oxidize, and grow acrid; the moisture dries away. Every thing volatile vanishes, and, at the end of a certain time, nothing remains save the skeleton, but a formless mingling of mineral principles, a sort of humus, ready to manure the earth. Now, all these complex operations absolutely required the intervention of the infusoria of putrefaction. In pure air, deprived of living germs, they could not have been accomplished. To check putrid fermentations, to insure the conservation of animal or vegetable substances in a state of perfect integrity, only one means avails, but that is an infallible one—that of thoroughly precluding the access to them of the aerial germs of vibrios and bacteria. Whether we adopt D'Appert's method and begin by subjecting these substances to the action of high temperature, preserving them after that in hermetically-closed vessels; or whether, as we have seen very lately practised by M. Boussingault, we introduce them into an extremely cold medium; or whether we saturate them with such salts as have antiseptic properties, in every case they are protected from putrefaction by paralyzing the effect of the lower organisms. The corruption of animals is not more possible than the fermentation of grape-juice, barley-wort, milk, etc., when it is made impossible for the germs to act. This is another fact demonstrated by M. Pasteur.

We have just used the term antiseptic, that is, capable of destroying germs, and preventing the action of ferments. The interest connected with such substances is easily understood. In truth, they are at the present time the chief objective point of therapeutic researches. At the same time that chemists and physiologists are engaged with persevering zeal in studying the functions of microscopic corpuscles in living Nature, physicians, perceiving their manifold and baneful activity in the production of disease, are seeking the means of reaching and destroying them. Every one knows those principles, like phenic acid, which are extracted from pitch, and are also found in smoke, to which they impart antiseptic properties that have been utilized from time immemorial. Other substances have been lately discovered, not less remarkable for their energetic resistance to fermentation and virus. Among the number are the alkaline sulphites and hyposulphites, which have been the object of very interesting examination on the part of an Italian physician, M. Polli; the borates and silicates of potassa and soda, to which M. Dumas invited the attention of physiologists a year ago; the acetate of potassa, and others. Hitherto the physiological virtues of active principles have been studied only with respect to the higher order of animals: M. Dumas pointed out the great interest there would be in examining the influence they exert over the lower organisms charged with the elaboration of ferments, and over ferments themselves. Such researches not only contribute to a better knowledge of the mechanism itself according to which these principles affect the system of vital phenomena, but they also gain the most useful indications for the healing art. Indeed, beginning with the moment at which M. Dumas and other chemists made known the result of their examinations on this subject, coincident also in time with the experiments of M. Davaine on septicæmia, a vast number of attempts were entered upon, in hospitals and in laboratories, to discover to what extent these anti-fermenting substances hinder morbid fermentations. These attempts are still proceeding; we cannot foretell their success, but we are authorized even now to say that they will not be barren of advantage to the healing art. In this, as in all other departments of scientific activity, we see abstract studies result in useful discoveries.

As a general statement of the subject, all this immense work of fermentations, putrefactions, and corruptions of organic matter, is effected in the world by a small number of species of microscopic cells and filaments, by fungi and spores of the lowest order, of which the germs fill our atmosphere. This is one of the most certain acquisitions of modern science, one of the most important from the point of view of natural philosophy, one of the most productive for those arts that are concerned in improving the condition of mankind. We may now regard it as firmly established; but let us not forget that its establishment has cost two centuries of investigations and labors. Leuwenhoek, in the middle of the seventeenth century, was the first to reveal the microscopic world of the air, and to conjecture its momentous functions. What severe toil, what struggles and tedious trials, since the observations of the Dutch micrograph, to the time of the experimental studies of our contemporary and compatriot, M. Pasteur!