sugar fermentation acid alcohol yeast vinous water juice ferment according
C12H2901,.H30 = 4C3H603. Milk Sugar. Lactic Acid.
Now, this in itself is nothing exceptional. A solution of cyanate of ammonia (NCOIINH8) is no sooner prepared than it passes into one of urea CO(N112)2; cyanic acid, (NCHO) when left to itself, soon passes into cyamelide, just as the milk sugar of the milk passes into lactic acid. But there is this great difference, that this latter change cannot be realized, under any known set of conditions, in a solution of pure milk sugar in pure water. And so it is in all other analogous cases. But this comes to the same as saying that fermentations, as a class of chemical reactions, are characteristically non-spontaneous, and consequently must be caused by reagents, although these reagents have no place in the mere balance-sheet of the reaction. In fact, experience shows that no fermentable chemical species will ferment except in presence of water, and unless it be kept by means of that water in direct contact with some specific "ferment," which, although it contributes nothing to the substance of the products which figure in the equation, nevertheless induces the reaction "by its presence," as the phrase goes. The presence alone, of course, will not do. It is simply inconceivable that a reagent should act chemically unless it were itself in a state of chemical change, although this change may be (and with some ferments probably is) a cycle of changes which always brings back the reagent to its original condition.
Of all the multitude of chemical processes which fall under our heading, vinous fermentation is the one which is by far the best known and most satisfactorily explained; and it is scarcely an exaggeration to say that the present science of the whole subject has been evolved from the study of that particular case. Hence the best course that we can adopt in this article is to begin with a popular exposition of the growth of our knowledge of vinous fermentation, which may familiarize even the general reader with the main points of the whole subject, and then to append a short epitome of the facts concerning the more important of the different fermentative changes.
Vinous fermentation means that peculiar change which all native sacchariferous juices are liable to undergo when left to themselves at the ordinary temperature, and which results in the formation of some kind of "wine." The general course of the phenomena being the same in all cases, we shall assume in what follows that it is grape juice we have to deal with. Such juice, as is well known, when recently prepared, forms an intensely sweet yellowish liquid, which, if it is not so by nature, may be rendered perfectly limpid and transparent by filtration through bibulous paper. Grape juice when left to itself, after having been thus clarified, may remain unchanged for an indefinite time, but when mixed with ever so little of unfiltered juice, it is sure sooner or later to undergo a change, which manifests itself in the appearance of a turbidity in the liquid. This turbidity is owing to two causes, namely, (1) the evolution of carbonic acid, and (2) the formation within the liquid of a finely-divided solid, which, through the gas-evolution, is partly kept in suspension, partly thrown up to the surface as a scum, and which is known by the name of "yeast." The process, from an almost imperceptible beginning, gradually develops into a more and more vivid effervescence (which not unfrequently assumes the character of a violent ebullition), the yeast at the same time becoming more and more abundant; and when a sufficient quantity of "must" is operated on, the temperature of the fermenting mass soon rises perceptibly beyond that of the surrounding air. Sooner or later of course the reaction reaches a climax, from which onwards it gradually loses in intensity until at last it dies out. The yeast then settles down as a slimy deposit, above which there is left a clear yellow liquid, which, instead of the originally sweet, now has a " vinous " taste, and is endowed with that well-known physiological action characteristic of " fermented liquors." Chemically the change in the nature of the liquid consists substantially in this, that the sugar has mostly or perhaps wholly disappeared, and given place to a corresponding percentage of a volatile inflammable liquid called alcohol. To any one who has a real knowledge of these facts it must necessarily suggest itself as a highly probable hypothesis that it is the destroyed sugar which has furnished the ingredients for the formation of the carbonic acid and of the alcohol, while most persons will be inclined to look upon the yeast as a bye product formed from the secondary constituents of the juices.
This view, which is endorsed substantially by our present knowledge of the matter, one is inclined to think should have forced itself even at the earliest times upon the minds all who reasoned on the process as a material metamorphosis. But although now-a-days everybody looks almost instinctively upon chemical reactions as nothing more than rearrangements of the ultimate ingredients of the bodies concerned, which ingredients in themselves are, as a matter of course, assumed to be uncreatable and indestructible, we must not forget that this notion dates back only to the time of Boyle, and that is not much longer than air, and gases generally, have been recognized as species of weighable matter. Hence for many centuries the carbonic acid was not recognized even by chemists as forming a factor in the chemical reaction ; it was known only as an effervescence, a phenomenon pure and simple, not as a substance. Van Helmont (born in 1577) was the first to show that the gas which rises from fermenting "must" is different from air, and identical with the gas sylvestre formed in the combustion of charcoal and in the calcination of limestone. Long before Van Helmont's time, the "alcohol" had been recognized as a definite kind of matter. The art of concentrating the intoxicating principle of wine by distillation, in fact, was known and practised industrially in the 8th century ; and nobody could practise this art without finding out that a spirit can be strengthened by repeated distillations, with elimination of water. But it was only about the 13th century that chemists learned to remove all the water from spirits of wine, and thus to prepare "absolute," that is, pure alcohol.
Ordinary cane sugar and honey were known to the ancients ; and chemists from the earliest times took it for granted that these two substances and the sweet principles in fruit juices must be closely related to one another. It is also an old experience that cane sugar or honey when added to grape juice ferments with the sugar originally present in the latter. But the idea that the differences between the several kinds of sugar are owing to the existence of a number of distinct chemical species is comparatively new, and it is only in the course of the present century that the problem of isolating these several species has been satisfactorily solved.
But to return to our proposition ; plausible as it is as an hypothesis, to be able to test even its potential correctness, we must know the weights of alcohol and carbonic acid produced in the fermentation of a given weight of sugar, and know also the quantitative elementary compositions of the three substances. Lavoisier was the first to make experiments for supplying these data, which, in fact, could not reasonably have been attempted by anybody before him, as it is ho to whom we owe our knowledge of the qualitative elementary composition of the substances concerned, and indeed of organic substances generally.
Before giving his numbers, it may be stated that he regarded acetic acid (a small quantity of which is present in most wines) as, like alcohol and carbonic acid, a constant product of vinous fermentation. According to Lavoisicr, 95.9 parts of cane sugar in fermenting yield And according to his elementary analysis of these substances, the proportions by weight are - From these numbers Lavoisier concluded (and he was quite justified in doing so, considering the imperfections of his methods of analysis) that sugar in fermenting simply breaks up into these three substances, without any access of matter from without. But if he thus managed to arrive at what we now know to be a substantially correct conclusion, this can be credited to him (if at all) only as a happy stroke of divinatory genius, as his numbers are all of them monstrously incorrect, the errors going far beyond what even, with his necessarily imperfect method, could be tolerated as " observational errors." Lavoisier's numbers were subsequently corrected by Gay-Lussac according to his own analyses of sugar, alcohol, and carbonic acid. his results, which have remained unimpugned to the present day, may be stated, with substantial correctness, to have been as follows :- In vinous fermentation very nearly one-third of the carbon goes off as carbonic acid, while the rest passes into the alcohol; and reducing to 1, 2, and 3 parts of carbon, we have Carhnn Tivtl ',non CP“runn The agreement being by no means satisfactory, Gay-Lussac suspected that his analyses of sugar were infected with unobserved errors, and he corrected his figures so as to make them agree with those given above opposite to "Sums." These values, when measured by the customary units (namely C for twelve parts of carbon, II for one part of hydrogen, 0 for sixteen parts of oxygen), assign to sugar the very simple formula C111,01 leading to an equally simple equation for the reaction, which is :- i.e., 180 of sugar gives 2 x 46 of alcohol + 2 x 44 of carbonic acid ; or 45 Pf PP 23 JP + 22 7, JP This equation is still looked upon as substantially correct, though not in Gay-Lussac's sense. It is so, if by sugar we understand either of the two kinds of "glucose" which form the bulk of the sweetening principles in fruit juices, and which are composed according to the formula C,11120„. Cane sugar, as Dumas and Boullay showed, really has the composition following from Gay-Lussac's analysis, which, as is easily seen, corresponds to the formula C121122011= 2C,1-11296 1-120, where 1120 means the elements of 18 parts of water ; and these 18 parts of water, as Dumas and Boullay showed, actually are taken up in the fermentation of C121122011 324 parts of cane sugar.
Gay-Lussac's equation being, as we said, only substantially correct, we must now state the qualifications implied. Schmidt of Dorpat found in 1847 that vinous fermentation always results in the formation of small quantities of suecinic acid. Guerin Vary showed, by quantitative experiments, that in the fermentation of glucose the alcohol and carbonic acid produced account only for about 96.3 per cent. of the glucose. And the present writer happens to know that a certain German apothecary made the interesting discovery that wines, beside the unfermented remnant of glucose that may be left, may contain an unfermentable sweet principle which he recognized as glycerine. These observations, however, were little heeded until Pasteur, in a now classical memoir, proved that glycerine and succinic acid are constant products of normal vinous fermentation, the correct balance sheet of the reaction, according to him, being as follows :-100 parts of cane sugar, in fermenting, pass into 105.4 parts of glucose, which then break up, yielding (approximately) of aUt/ But even this is not quite an exhaustive statement, a small portion of the sugar always passing into the form of higher alcohols (" fusel-oil") and compound ethers.
Vinous fermentation, then, is a far more complex reaction than Gay-Lussac imagined ; but it still remains true that all the products formed are derived from the dissociation of the sugar. What is it that brings about this singular decomposition 1 We call it a singular reaction, because it is one which sugar has never been seen to undergo when subjected by itself or as an aqueous solution to the action of heat or electricity or any ordinary reagent. And we have theoretical grounds for presuming that the reaction is not likely ever to be realized by some "reagent" that has not yet been tried. According to many experiences, an arithmetically possible reaction is the more likely to be realized the greater the heat evolution which, supposing it were realized, it would involve. Now, the reaction formulated in Gay-Lussac's equation C, /1120s = 2002+ 2021160, as Professor Dewar pointed out some years ago, supposing dry sugar could be made thus to split up, would yield only an insignificant amount of heat, if any. Actual fermentation does involve a liberation of heat, as we know, but the quantity of heat per unit weight of sugar destroyed, according to Dewar's experiments, amounts only to about 83 heat-units, which can be accounted for as being produced by the hydration of the alcohol formed, and, at any rate, is too small to characterize the decomposition of sugar into carbonic acid and alcohol as being at all of itself a probable reaction. Even the somewhat higher result previously arrived at by Dubrunfaut, namely, 135 heat-units per unit of sugar, cannot affect this conclusion. Before going further let us take an exact survey, from the chemical standpoint, of the conditions which are known to favour or impede the actual process.
Pure solutions of cane sugar or glucose do not ferment under any circumstances.
Many kinds of impure sugar solutions, such as grape juice, brewers' wort, &c., do ferment. The range of temperatures most favourable to this process lies between about 20° and 24' C. (or 68° and 75° F.). But even grape juice does not ferment at temperatures lying too close to the freezing-point, nor does it ferment at tempera- tures exceeding a certain limit, which lies at about 60° C. (140° F.). The most lively fermentation comes to a stop when the liquid is boiled, and, after cooling, it takes a longer or shorter time before it resumes.
Grape juice which has been strengthened by evaporation or addition of sugar from without, does not ferment, when the ratio of water to sugar falls below a certain limit-value.
Fermentation is impeded and may be entirely stopped by addition of alcohol. Hence the wines produced from the rich juices of southern grapes always contain unfermented sugar.
Fermentation may be stopped more or less completely by addition to the liquid of even small quantities of certain reagents called antiseptics. Of these corrosive sublimate (and many other heavy metallic salts), sulphuric acid, sulphurous acid, bisulphide of carbon, and carbolic acid may be mentioned as examples.
Perfectly pure grape juice does not ferment, unless the process has been started by at least temporary contact with ordinary air. This cardinal fact was discovered by Gay-Lussac in a now classical series of experiments. Ho caused clean grapes to ascend through the mercury of a large barometer into the Toricellian vacuum, where he crushed them by means of the mercurial column. The juice thus produced and preserved remained unchanged ; but the addition to it of ever so small an air-bell (as a rule) induced fermentation, which, when once started, was always found to take care of itself.
Ordinary vinous fermentation al ways involves the formation of yeast. This is the most important of positive facts made out.
(S.) The rate at which a fermentation progresses is (in a limited sense) determined by the quantity of yeast present within the liquid.
(9.) Spontaneous fermentation of grape juice is always slow in beginning ; addition of yeast from without starts it immediately.
From these facts it is legitimate to conclude that it is the yeast or some constituent of the yeast which somehow at once follows that the ferment must be sought for amongst the insoluble portion of the yeast.
Their non-success in isolating the vinous ferment did not prevent chemists from speculating on its mode of action. Berzelius gave it as his opinion (which was adopted by Mitscherlich and others of the leading chemists) that the action was a purely "catalytic" one. What he meant by this is best explained by an example. Peroxide of hydrogen (a compound of the elements of water and oxygen) is perfectly stable at ordinary temperatures. Add to it a mere speck of platinum black (a peculiar form of finely divided platinum), and it at once breaks up into water and oxygen, the platinum which caused the decomposition remaining unchanged. In an exactly similar manner Berzelius thought the yeast acted upon the sugar, and caused it to break up into alcohol and carbonic acid. The merit of the idea was that it apparently reduced the explanation of a seemingly complex to that of an undoubtedly simpler phenomenon. But unfortunately neither Berzelius nor any of his followers succeeded in proving the objective existence of the analogy by experimental evidence. Hence Berzelius's theory really amounted to no more than showing that vinous fermentation and the " catalytic " reactions of inorganic chemistry were both unexplained phenomena.
Something far more worthy of the name of a theory had been offered 200 years before by Stahl. The originator of the phlogiston theory justly divined that vinous fermentation and putrefaction are phenomena of the same order, and, starting from the well-known infectious nature of the latter, explained both as disturbances in the "molecules" of the fermenting body, brought about by a pre-existing molecular motion. "Fin Korper der in der Faulung begriffen ist bringet in einem anderen von der Faulung annoch befreiten sehr leiehtlich die Verderbung zu Wege, ja es kann ein solcher, bereits in innerer Bewegung begriffener Korper cinen anderen annoch ruhigen, jedoch zu sothaner Bewegung geneigten sehr leicht in eine solche innere Bewegung hineinreissen."
These ideas of Stahl's, at the time of Berzelius's catalytic theory, had long been forgotten, and they remained lost to science until they were revived and brought into a more definite form by Justus Liebig, who, in a powerful and comprehensive memoir on fermentative changes, which he published in 1848, used them as the basis of a new theory of these phenomena, which justly attracted universal attention, as it - or rather the wonderfully lucid memoir which embodied it - exhibited the subject in a clearer light than anything else that had been said or written on it before. With Liebig as with Stahl, all " fermentations" and " putrefactions " are analogous phenomena. Putrefactions are owing mainly, to the inherent instability of the albuminoid constituents of the respective substances in presence of water. So unstable are these albuminoids that even an incipient oxidation (see Gay-Lussac's experiment) may suffice to disturb their chemical equilibrium to such an extent as to cause the whole of the atoms of the mass to gradually rearrange themselves into new products of lesser complexity and consequently higher stability. The decomposition when once started, readily propagates itself through the whole mass, aided as it is by the inherent tendency of the molecule to pass into more highly stable forms, just as a stone which rolls down a hill and strikes other stones on its way causes them to roll clown likewise. This is so clear and plausible as almost to command assent. It is less easy to agree with Liebig when he tries to explain fermentation, when he says, for instance, that the sugar in grape juice, although not naturally gravitating towards a rearrangement as alcohol plus carbonic acid, is nevertheless caused to undergo this change by its immediate contact with the albuminoids of the juice or yeast, which are in a state of atomic commotion; and it is still less easy to see how such an atomic revolution could progress from sugar to sugar, as he says it may. That the nitrogenous matters of the juice, in all ordinary cases of vinous fermentation, assume the form of yeast, is, according to Liebig, a purely accidental phenomenon, and, if yeast is so characteristically powerful as a ferment, it is so only through its ...consisting largely of exceptionally unstable albuminoid substances.
Liebig's ideas, more perhaps through the brilliancy of his mode of exposition than the force of his arguments, took firm hold of the scientific mind of the time ; amongst chemists at least the general impression was, and it prevailed for a considerable time, that Liebig's theory in a satisfactory manner summed up the whole of the empirical knowledge of the subject - although it totally ignored at least one most important feature in tho phenomena which had been brought out and firmly established by Schwann and Cagniard-Latour.
In 1680 a Dutch philosopher, Leuwenhoek, fell upon examining yeast under the microscope, and found it to consilt of minute globular or ovoid particles. Microscopes in his time were very imperfect or he would have made a great discovery. Schwann and Cagniard-Latour, who (about 1838, and independently of each other) resumed the old Dutchman's inquiry, used the better instruments of their time, and discovered that Leuwenhock's globules are membranous bags, which exhibit all the morphologic characteristics of vegetable cells, and, like these, when brought under the proper conditions, increase and multiply in the biologic sense. Taking this together with the long known fact that in vinous fermentation the yeast increases as the process progresses, they naturally concluded that yeast is a species of plant, and that it is the life of that plant which somehow or other causes the chemical change. It is the special merit of Schwann to have adduced powerful experimental evidence in favour of this view. In his case, the observations on yeast were incidental only to a more comprehensive investigation, the original aim of which had been to solve the great question of spontaneous generation. Processes of putrefaction having long been known to be invariably accompanied by the formation of vibriones and other microscopic organisms endowed with voluntary motion, he prepared infusions of flesh and other putrescible matters in glass flasks, and, after having hermetically closed these, exposed them for a time to the heat of boiling water, so as to destroy every trace of living germs that might be present. The contents, when preserved in that condition for ever so long, showed no sign of putrefaction or of life of any kind. But when exposed to the air they did putrefy, and soon swarmed with living organisms of various kinds. Obviously it was the air which caused this two-fold change. But then the air which had been shut up with the infusions did not act. This, however, might have been owing to an absorption of the oxygen by the juices. Sehwann therefore, in another set of experiments, allowed the boiled (and consequently germless) infusions to communicate freely with the atmosphere, in such a manner, however, that no particle of air could enter the flasks without having first passed through a red-hot glass tube, and thus been freed from any germs that might float about in it. In this case the air had fair play in a chemical sense, but yet, not only did no life of any kind make its appearance, but even the chemical changes failed to set in. Exactly similar results were obtained by Schwann in experiments with grape juice, whether previously mixed or not with yeast. Gay-Lussac's famous experiment failed when the air-bell, before being admitted to the juice, had been heated, and thus freed from living germs. In a few of these experiments, it is true, the results were contradictory to the general evidence afforded by the rest of the work. But Schwann had no doubt in his mind about the close analogy between vinous fermentation and putrefaction ; and as the putrefaction experiments had all given one and the same answer, he explained these anomalies as having been caused by unobserved slips in the respective experiments, and did not admit them to invalidate his general proposition that both putrefaction and fermentation are inseparably connected with characteristic biologic phenomena ; - the less so, as his experiments on the action of certain antiseptics had shown that what is an " antiseptic " to a fermentative change is a poison to the organisms characteristic of the case. Thus, for instance, he found that white arsenic1 and corrosive sublimate, being poisonous to both plants and animals, stop both putrefaction and fermentation ; while extract of nux vomica, being destructive of animal but not of vegetable life, prevents putrefaction, but does not interfere with vinous fermentation.' The mechanism of the latter process he imagined to consist probably in this, that the " sugar-fungus' (the yeast) lives at the expense of the nitrogenous matters and of the sugar of the juice, and that those of the elements of these substances which the plant does not assimilate are eliminated chiefly as alcohol. This special theory of Schwann's, as the reader is aware, is not quite correct, but it does not affect his general views on the phenomenon, which were fully confirmed by subsequent investigators. Amongst these we may mention Helmholtz, who showed that oxygen evolved by electrolysis from water does not, like air, induce vinous fermentation. The same observer showed that boiled grape juice, when tied up in a bladder, does not ferment, even when suspended within a tub full of fermenting juice. The evidence afforded by this experiment was considerably strengthened by Mitscherlieh, who proved that even a septum of filter paper effectually stops the propagation of the reaction. More striking still is an experiment which was made, many years later, by II. Hoffmann. He took a test-tube full of sugar water, and by a plug of cotton wool inserted within it divided the liquid into two parts. To the upper part he added yeast, which of course induced fermentation there ; but the change did not propagate itself through the cotton wool to the lower portion. The same material had done good service some years before in the hands of Schroder and Busch, who proved in 1854, by a most extensive series of experiments, that the something in air which enables it to start fermentative changes in boiled infusions of meat or malt, in grape juice, can be effectually removed by filtration of the air through cotton wool. It is true the "&c." here does not include milk, which they found to turn sour in filtered as well as in ordinary air, but this exception was subsequently explained away by Pasteur, who found that germs immersed in alkaline liquids may survive temperatures considerably higher than 100° C.
A number of other important researches, which led to substantially similar results, must be passed over here, and may be, because what we have quoted has never been disproved, and is consequently quite sufficient to show that, in the case of vinous fermentation and putrefaction at any rate, those atomic motions, which, according to Liebig, cause the disintegration of the fermenting substances, - if the notion is to be maintained at all, - cannot be admitted to have an existence outside the living bodies of certain organisms characteristic of the respective changes. To any unprejudiced person this would appear to be sound logic ; but Liebig did not see it, and for a long time he had the majority of chemists at least on his side. No reasonable person could have denied the irresistible force of the arguments of Schwann and his followers ; but these chemists somehow or other managed to ignore the facts, until Pasteur, by means of a most thorough and extensive experimental research (of which the principal portions were published from 1857 to 18G1), simply forced the attention of everybody to the physiological side of the subject, and, by absolutely unimpeachable evidence, proved that Schwann's views are substantially correct. Of this investigation it is impossible to speak otherwise than in terms of the highest admiration. Even the purely critical portion of Pasteur's work would be enough to immortalize his names He did the whole of the work of Schwann and the rest of his predecessors over again, modifying and perfecting the experimental methods, so as to silence any objection or doubt that might possibly be raised, repeating and multiplying his experiments until every proposition was firmly established. But his work was synthetical as well as analytical. Some of his discoveries will be noticed below ; suffice it here to mention one of the general results which he arrived at. Vinous fermentation is only one of a number of fermentative changes to which sugar is liable. The same substance sugar, which, when placed under certain conditions, breaks up into alcohol and carbonic acid, under certain other sets of conditions ferments into lactic acid, or through lactic into butyric acid, or into gum plus marmite. This has long been known. What Pasteur showed is that each of these changes is the exclusive function of a certain species (or at least fourth for butyric fermentation. No two of these species, narrow and bent like a gas-evolution tube, the other short first the tubulus by means of a (germless) glass stopper, introduce a speck of the yeast through the tubulus, which, ture which is most favourable to the development of " saccharomyces." The saccharomyces-cells, being in the majority and enjoying a position of advantage, will multiply at a greater rate than the foreign cells, of which many in fact will go to the wall, so that what we ultimately obtain general, was already a little better (in all probability) than supply of germless wort, and so on until the foreign cells yeast, is liable to.
After Pasteur's researches it became impossible not to go no further than to admit that those living organisms are the only known sources for the ferments proper, which in themselves are chemical substances pure and simple.
Proceeding now to give a short account of the different fermentative changes, we begin with those that are proved to be functions of purely chemical reagents.
A. _Fermentations proved to be purely chemical reactions.
These are conveniently arranged according to the respective cute. ]ytic agents.
organic substances, when boiled with water and a small quantity of sulphuric, muriatic, or other strong mineral acid, undergo hydration and decomposition, or other chemical transmutation, the acid remaining ultimately in its original condition. Thus, under the circumstances named, - Cane sugar is "inverted," i.e., converted into dextrose and levulose, thus : The same equation applies to the case of milk sugar, one of the products 06111206 in this case being a peculiar substance called. " galactose."
Starch passes into dextrine (a kind of gum) and dextrose, thus: Many other "glucosides" (native substances containing potential glucose) behave in a similar manner. The exact mechanism of these reactions is scarcely understood ; pending exact investigations, they may be explained, according to Lyon Playfair, by a tendency of the acid to combine with the elements of one of the products, which tendency, although sufficient to sever these elements from the rest, is defeated ultimately by the stability of the compound formed by their union with one another.
Diastase is a peculiar substance which is formed in the germination of grain (in malting), and which has the power of converting many times its weight of starch into dextrine and dextrose when made to act on it in the presence of water at about 66° 0. Diastase has not yet been isolated in the pure state. In the process referred to it is changed ; but it is not known into what.
Emulsi7w is a constituent of almonds (both of bitter and sweet), which is known chiefly for its power of decomposing amygdaline (a crystalline substance contained in bitter almonds, and extractable therefrom by alcohol), with formation of bitter-almond oil and glucose, thus : The oil, as the formula shows, is a (loose) compound of prussic acid, NCH, and benzaldehyde, 071160. The common idea that bitter almonds contain prussic acid is erroneous ; that acid, like the benzaldehyde, is present only potentially, viz., as amygdaline, which, when the almond meal is treated with water, undergoes the above fermentative change. Many other gbicosides are decomposed by emulsine, as they are by dilute acids. It may be said, in passing, that the acrid volatile oil contained in table-mustard is not found ready formed in the mustard seed, but is produced from a constituent of the seed by a fermentative action closely analogous to that we have just; been explaining.
Soluble Yeast Fcrment. - It has already been stated that an aqueous extract of yeast, though devoid of the power of inducing vinous fermentation, converts cane sugar into dextrose and levulose. The ferment, as Berthelot showed, can be precipitated from the liquid, in an impure state, by addition of alcohol.
Pepsine. - Stomach digestion (in man and animals nearly related to man) consists mainly in this that the gastric juice dissolves the albuminoids of the food, as hydroehlorates of peptones, the only form, it seems, in which they can be assimilated by the system. The juice owes this power to the presence in it of small percentages of two things, namely, of free hydrochloric acid and of "pepsine," both of which are continuously produced by the mucous membrane. Real pepsine has never been seen ; but an impure substance, possessing the specific properties of the ferment, can be extracted from the mucous membrane of the stomach by a laborious process which we have no space to describe. Highly dilute hydrochloric acid alone dissolves certain allmminoids, but it does not convert them into peptones ; it acquires this property by the addition to it of a small quantity of the, preparation named. It is as well to state in passing, that the so-called pepsine of the pharmaceutist is only a very poor apology for even the pepsine of the physiological chemist.
Panereatine. - What pepsine is to the gastric juke pancreatine is to the secretion of the pancreas gland, whose function. it is to digest the starchy and fatty portions of the food. This " panereatine" seems to include three ferments, namely, a kind of diastase (see above), a ferment similar in its functions to pepsine, and a fer- ment which. has the power of converting fats into fatty acids and glycerine. None of these has been isolated.
Erythro:vme. - This is a peculiar ferment which Edwapd. Schunek, in .1854, extracted from madder-root, and which was found by him to possess the power of inducing vinous fermentation in solutions of sugar, - a most important discovery, which ought to be further investigated.
Kole. - All these ferments, the acids of course excepted, lose their efficacy at temperatures near 100° C. in presence of water, In the dry state they may survive boiling heat.
B. Fermentations uhieh are known only as I'hysioloyical Processes.
I. Vinous Fermentation. - This case having already been considered, we confine ourselves here to a few additions and qualifications. Vinous fermentation, as we see it going on in the brewers' vats and in the wine-producers' casks, is a function of Saccharomyces, a genus of fungi, consisting of minute cells, which sometimes are isolated from one another, sometimes grouped together in a variety of forms, but never united into OM organized tissue. There is a variety of species, of which S. eererisite (the main constituent of ordinary yeast, as produced in the high fermentation of beer) is the most important. It consists of cells of about h millimetre diameter. According to Pasteur, saccharomyees thrives best when immersed in grape juice or wort, or similar liquids. It multiplies only by budding, never by sporification. In pure sugar-water it lives, so to say, at its own expense, and gradually becomes exhausted ; but on addition of phosphates (yeast-ash works best) and ammonia salt to the sugar, the plant thrives as well almost as in native sugar juices. 11 hen saccharomyces is not fully immersed in the liquor, and otherwise constrained to live under abnormal conditions, it passes into "aerobiotic" forms which are similar to inucors and mucedos (mould plants), and which, like these, live on atmospheric oxygen. But these abnormal forms, when re-immersed in wort, &c., always relapse into the non-aerobiotic form of saecharomyees. Real mucedos, &c., for instance Mycoderma and errerisiw, which by nature are aerobiotic, when immersed in wort or grape juice, and thus placed in what to them is an abnormal condition, assume non-ae•obiotic forms, and produce vinous fermentation, but (contrary to what was formerly assumed by Pasteur himself) they are never converted into saccharomyces, and their fermentative rower soon comes to an end, unless they are occasionally revived by rc.exposure to the atmosphere.
The power of inducing vinous fermentation, however, is by no means confined to microscopic organisms. It has long been known, from the experiments of Diibereiner and others, that sweet fruit, when kept within an inert atmosphere devoid of free oxygen, evolves carbonic acid with formation of alcohol, and it has been proved by Pasteur that this fermentation, which may extend to a consider'ablo portion of the sugar present, is not accompanied by the development of any microscopic species. Closely related to this fact is the well-established experience that large quantities of sugar may be made to ferment by means of yeast without the latter multiplying to any noteworthy extent. On the other hand, large growths of yeast may Imo obtained (and as a matter of fact are obtained every day by the makers of German berm) without producing much alcohol. Oskar Brefeld, by means of a peculiar artifice, succeeded in growing sacclutromyees in brewers' wort, without producing a trace of alcohol. From these experiences wo must conclude that vinous fermentation, fa'r from being the characteristic life-function of healthy saccharomyces, is dependent on a certain pathologic condition of "non-photobiotic" plant-cells (i.e., cells which habitually live in darkness) generally, which is brought about by immersing them in saccharifcrous fluids and shutting them out front the oxygen-gas which they need for their healthy development. Hence, even in the ordinary cases of fermentation, the normal life of the yeast-plant on the one hand, and the dissociation of the sugar on the other, are not only not necessarily related, but, in the individual cell, positively exclude each other. In any given mass of yeast, healthy cells and diseased cells are in general mixed up together, and thus, in practice, the two phenomena come to be accidental concomitants. But this brings us back almost precisely to the later views of Liebig, as set forth in his last memoir on the subject.
In regard to the genesis of the yeast plant little is known. According to Pasteur's experiments and observations the yeast which forms spontaneously in grape juice is derived chiefly front certain germs which abound about harvest time on the grapes, and still more on the grape-stalks. These germs are largely diffused also through the atmosphere of breweries, wine cellars, and laboratories where fermentation experiments are carried on, but they are not by any means widely diffused through the atmosphere generally.
The milk sugar, before assuming the form of lactic acid, probably passes through the condition of glucose. At any rate, ordinary glucose, when dissolved in milk, ferments into lactic acid along with the milk sugar originally present. But in this case, if the total percentage of sugar goes beyond a certain limit, the reaction comes to a stop as soon as the acidity of the liquid has attained a certain limit-value. Addition of chalk or carbonate of soda, i.e., conversion of the lactic acid into a neutral lactate, then revives the process. A solution of "invert-sugar" (as produced by boiling cane sugar water with a little vitriol), when mixed with excess of chalk and some putrid cheese, and kept at 30*--35* C., soon ferments, with formation of large quantities of lactate of lime (Hensel). Lactic fermentation, according to Pasteur, is caused by the development in the mass of a microscopic fungus, consisting of cylindrical cells which are far smaller than those ot' saccharomyees. We are not au•are that this "lactic ferment" has ever been seen in ordinary sour milk ; in Borsch's process it is produced largely as a greyish deposit on the chalk, from which pure growths of the fungus may be obtained by Pasteur's method (see above). The lactic ferment, to the annoyance of brewers, frequently occurs in ordinary yeast as an impurity, There is no doubt that that fungus which Pasteur calls the lactic ferment is capable of inducing lactic fermentation ; but it does not by any means follow that it is the thing which actually causes the souring of milk under ordinary circumstances. On the contrary, from a remarkable set of experiments made by Lister in 1872, this appears not to be the case. According to him, milk can be completely purged of germs by exposing it (within a germ-less flask) to the temperature of boiling water for some hours, and, when protected against atmospheric germs by a slightly earbolized stopper of cotton wool, keeps sweet for an indefinite time. Specimens of such ge•mless milk, when exposed to time atmosphere of his study, were found by Lister to undergo a variety of fermentative changes, accompanied sometimes by the development of an acid reaction, but none of them set into sour milk. A specimen of ordinary unboiled dairy milk when kept in the same room did get sour as usual, and, when examined under the miscroscope, was found to contain, not Pasteur's fungus, but a kind of motionless bacterium which Lister calls B. lactis, because the introduction of it (or rather of a trace of the sour milk containing it) into the gormless milk determined normal lactic fermentation, the Bacterium lactis multiplying at the same time. The same bacterium, when made to pass successively through germless urine and other gormless organic liquids, underwent a series of metamorphoses, but, when ultimately put back into milk, caused normal lactic fermentation. The germs of this bacterium must be assumed to abound in the atmosphere of cows' stables and dairies, although they do not seem to be abundantly diffused through the atmosphere generally.
Viscous Fermentation is a peculiar change which has long been known to occasionally accompany vinous fermentation, and which manifests itself in this that the wine becomes thick and viscous, so that, when poured from one vessel into another, it draws into long threads. This property is caused by time presence of a kind of gum (of the composition 012112„010) which is invariably accompanied by marmite, a sweet crystalline substance of the composition C,11 (i.e.containing the elements of glucose, 00111,06+ those of hydrogen, 1I2). The exact nature of the reaction is not established ; in fact, we do not know whether it is one reaction or a set of reactions going on simultaneously. According to the usually adopted equation, 100 parts of cane sugar should yield 61 of mannite, 45'5 of gum, and 6 of carbonic acid. According to Peligot (supported by Pasteur) the "viscous ferment" is a fungus consisting of very minute spherical cells (of 0.001 to 00014 millimetre diameter).
Butyric Fermentation. - In the lactic fermentation of glucose, as induced by milk or cheese in the presence of chalk, the lactate of lime is 110 sooner formed than it undergoes itself a further change, which. chemically. is represented annroximatelv by the collation The temperature most favourable to the change lies near 40° C. A number of similar changes (of other organic acids than lactic) are known, but they are passed over here, being of a more purely scientific interest. According to Pasteur, butyric fermentation is caused by the development in the mass of a special kind of vibrio, a wo•m-shaped animalcule, consisting of a number of longitudinal cells, each about 0.002 millimetre thick, and from 0.002 to 0'02 mm. long. Butyric fermentation, strictly speaking, is only one of a large genus of changes customarily summed up under the generic name of putrefaction.
Putrefaction. - The scientific meaning of this term coincides pretty much with its popular acceptation, except that it must be understood to be exelusiveof all cases of oxidation. In olden times it was assumed that organized matter (the tissues of plants and animals, blood corpuscles, Ste.) could hold together even chemically only as long as supported by the vital force. But this is a long exploded notion. In absolute absence of water, or at very low temperatures, dead organized matter remains chemically (and even structurally) unchanged. In support of this assertion we need only refer to that well known case of the mammoth of the Siberian cave, which was found sweet and fresh thousands of years after the extinction of life. And since the time of Appert (who discovered the now so extensively used process of preserving meats in sealed-up tins) we know that prolonged exposure to boiling heat and subsequent absolute i exclusion of air prevent putrefaction, even n presence of liquid water and at the ordinary temperature, as long as the air remains excluded. Chemically speaking, ordinary putrefaction is a most commdex phenomenon, always involving the simultaneous on-going of a multiplicity of chemical reactions. A comparatively simple ease is the putrefaction of urine, which substantially consists in this that the urea, by assimilating water, passes into carbonate of ammonia, just as it does when heated by itself with pure water to high temperatures. In the case of animal tissues, which, broadly speaking, may be said to consist of fats and albmninoids, the latter always give way first. Their decomposition is a most complex set of successive reactions, - leucine, tyrosine, fatty acids, and many other things appearing as primary products, ammonia, compound ammonias, sulphuretted hydrogen, hydrogen, and nitrogen as secondary ones. Less rapidly, but none the less constantly, the fats are changed, being decomposed, in the first instance, into fatty acids and glycerine, which latter undergoes further transmutations, while the former survive for a considerable time. The "adipocere" which is so well known as one of the constant ultimate products of the decay of dead bodies that have been kept from the air, and which consists of pahnitate and stearate of lime (Hoppe-Seyler), well illustrates the high stability of fatty acids. Regarding the causes of putrefaction, we can scarcely do more than refer to what we have quoted from the researches of Schwann and his followers. From these researches two things are clear, namely, (1) that putrefaction is not possible under conditions precluding the development of life, or, in other words, that there is no putrefaction where there is not at least potential life ; and (2) that in 999 out of a thousand cases this potential life assumes the actual form of bacteria and vibriones.1 Entrefactions going on in presence of air are always accompanied by processes of oxidation., the effects of which are difficult to differentiate absolutely from those of putrefaction pure and simple.
C. Cases of Oxidation.
Alcohol. Aldehyde. Water.
This aldehyde, however, in ordinary acetous fermentation never actually appears, being at once oxidized by the direct action of the air into acetic acid, thus : C2H40 + 0 = C211402 Aldehyde. Acetic acid.
These two reactions can be realized in all their chemical simplicity, not, it is true, by oxygen-gas pure and simple, but easily by oxygen as condensed on platinum-black ; and as the deoxidized platinum-black readily reabsorbs oxygen from the air, a small quantity of this reagent suffices to oxidize large quantities of alcohol into acetic acid by means of atmospheric oxygen. Upon this observation of Dobereiner's Sehiitzenbach based a rapid and practical method of vinegar-making, which consists in this, that the dilute alcohol is made to trickle through a tower of beech-wood shavings, packed into a tall barrel, constructed so as to draw in an ascending current of air. When a temperature of 20° C. is maintained in the room, and the spirit introduced having a temperature of 26', the temperature within the barrel is found to rise to 38'-40°, the heat being produced by the rapid oxidation of the alcohol into acetic acid. What, in the old method of vinegar-making, required weeks or months is thus accomplished in a clay or even less. It is difficult to avoid the conclusion that in Schiitzenbach's process the wood-shavings, besides serving to spread the alcohol over an immense surface, act exactly as the platinum-black does iu Raueiner's experiment, condensing oxygen in their pores in order to hand it over to the alcohol. And, supposing this theory to be correct, the old process, which consists in exposing the wine to the air in half-filled tubs or casks, would appear to rest on the same Principle, - the wood of the cask acting as the shavings do in Schiitzenbach's process, only far more slowly. But then it is an old experience of vinegar-makers that the old process at least always involves the formation of two organized products, namely, that of a kind of mould which appears on the surface as a membrane, and goes by the name of "flowers of vinegar," and that of a mucilaginous mass within the liquid, called " mother of vinegar ; " and it has always been admitted that the presence of these substances materially accelerates the process of oxidation. This, however, is no contradiction to the theory ; it would only prove that the mould-membrane and the mucilaginous mass are more effective carriers of oxygen than the wood of the tub. Besides, in Schiitzenbach's process, the shavings, according to experience, work the better the freer they are of from organized deposits. Hence, one might say, with Liebig, that the efficacy of these substances is a function only of their physical and chemical condition, the presence of life fu the mould plant being purely accidental and immaterial to the process. According to Pasteur this view is a mistake. With him it is the membranous mould on the surface of the fermenting liquid which hands the oxygen to the alcohol, and it does so only when it consists of living specimens of a certain species of mould-plant which he calls Myeoderma aceti. Other moulds or dead ..ilycoderma aedi do not work. Mother of vinegar, according to Pasteur, is the " non-aerobiotic " form of the mycoderma. Only the aerobiotic form acts. To keep it alive we must take care that the liquid contains the phosphates and the albuminoids or ammonia, winch it needs as food. lint, if it is to produce vinegar, it must not be fed too liberally, because, when in a vigorous state of health, it oxidizes the alcohol into carbonic acid and water. If the oxidation is to stop at acetic acid, the mycoderma must be in a peculiar abnormal condition,which may be ensured by the presence in the liquid of a certain limit percentage of alcohol. In the case of Sulditzenhach's ',recess, Pasteur maintains (in spite of apparently contrary experience) that it is the very same Mycodcrma accti which enables the wood shavings to act. One of his arguments is the acknowledged fact that Schiitzenbach's towers require to be started with ordinary vinegar,although they can be worked with distilled spirits. A more powerful argument he derives from the following experiment. A very slow current of dilute alcohol was caused to trickle down a long string suspended in a room kept at the most favourable temperature to acetous fermentation. The alcohol failed to assume an acid reaction. But the slightest coating of .illycodcrma accti attached to the string caused it to act exactly as the shavings do in the Schiitzenbach casks. After all, however, it is a little difficult to believe that the many pounds of alcohol which, in the course of a day, pass through a Schtitzenbach tower and come out below as acetic acid, have all been under the direct influence of the few grains of dlycodcnima (tea which a microscopist might hunt up amongst the wood shavings. It appears far more rational to assume that the mycoderma acts only indirectly, perhaps by converting a small portion of the alcohol into aldehyde, which diffuses itself through the whole mass of the alcohol, and, through its inherent attraction for oxygen atoms, which is assisted by a similar tendency in the porous wood, reduces the stability in a far larger number of oxygen molecules than it needs itself, to such an extent that these so to say half-liberated oxygen atoms become available for the oxidation of alcohol, the more readily as the reaction itself involves a considerable liberation of energy.
TEEM°, the ancient FirM212M PiCe11211, an archiepiscopal city of central Italy, and the chief town of a circle in the province of Ascoli Piceno, 31 miles S. by E. of Ancona. From its situation on a rocky height it commands a splendid prospect of the surrounding country, including a fine view of the Adriatic Sea. It is surrounded by old walls, and besides the cathedral possesses numerous churches and convents, a university, and two fine collections of statuary and paintings. The ruins of the ancient Roman town, which was destroyed in the 5th century, are still to be seen, Lactantius and Galeazzo Sforza were born in Fermo. The port, Porto di Fermo, is situated on the Adriatic, about four miles from the town. The harbour is small, but there is some trade in corn, silk, and woollens. The population of Fermo in 1871 was 7002.