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SCIENTIFIC NEWS. 



[Sept. 7, 1 J 



in the same way as in the animal economy. Take such a simple 

 case as a potato tuber. This is a mass of cellular tissue, the cells 

 of which are loaded with starch. We may either dig up the tuber 

 and eat the starch ourselves or we may leave it in the ground, in 

 which case it will be consumed in providing material for the growth 

 of a potato-plant next year. But the processes by which the in- 

 soluble starch is made available for nutrition are, I cannot doubt, 

 closely similar in either case. 



When we inquire further about these mysterious and all-important 

 bodies the answer we can give is extremely inadequate. It is very 

 difficult to obtain them in amount sufficient for analysis or in a state 

 of purity. We know, however, that they are closely allied to albu- 

 minoids, and contain nitrogen in varying proportion. Papain, which 

 is a vegetable ferment derived from the fruit of the papaw, and 

 capable of digesting most animal albuminoids, is said to have the 

 same ultimate composition as the pancreatic ferment and of pep- 

 tones, bodies closely allied to proteids ; the properties of all three 

 bodies are, however, very different. It seems clear, nevertheless, 

 that ferments must be closely allied to proteids, and like these 

 bodies, they are no doubt directly derived from protoplasm. 



I need not remind you that, unlike other constituents of plant 

 tissues, protoplasm, as a condition of its vitality, is in a constant 

 state of molecular activity. The maintenance of this activity in- 

 volves the supply of energy, and this is partly derived from the 

 waste of its own substance. This "self-decomposition" of the 

 protoplasm liberates energy, and in doing so gives rise to a number 

 of more stable bodies than protoplasm. Some of these are used up 

 again in nutrition ; others are thrown aside and are never drawn 

 again into the inner circle of vital processes. In the animal 

 organism, where the strictest economy of bulk is a paramount neces- 

 sity, they are promptly got rid of by the process of excretion. In 

 the vegetable economy these residual products usually remain. And 

 it is for this reason, I may point out, that the study of the chemistry 

 of plant nutrition appears to me of such immense importance. The 

 record of chemical change is so much more carefully preserved, and 

 the probability of our being able to trace the changes it has followed 

 is consequently far more likely to be attended with success. 



This preservation in the plant of the residual by-products of 

 protoplasmic activity no doubt accounts for the circumstance which 

 otherwise is extremely perplexing — the profusion of substances 

 which we meet with in the vegetable kingdom to which it is hard to 

 attribute any useful significance. It seems probable that ferments 

 in a great many cases belong to the same category. I imagine that 

 it is in some degree accidental that some of them have been made 

 use of, and thus the plant has been able to temporarily lock up 

 accumulations of food, to be drawn upon in future phases of its life 

 with the certainty that they would be available. Without the fer- 

 ments the key of the storehouse would be lost irretrievably. 



Plants, moreover, are now known to possess ferments, and the 

 number will doubtless increase to which it is difficult to attribute 

 any useful function. Papain, to which I have already alluded, 

 abounds in the papaw, but it is not easy to assign to it any definite 

 function ; still less is it easy, on teleological grounds, to account for 

 the rennet ferment contained in the fruits of an Indian plant, 

 Withania coagulans, and admirably investigated by Mr. Sheridan 

 Lea, 



Having dwelt so far on the action of ferments, we may now turn 

 to fermentation and that other kind of change in organic matter 

 called " putrefaction," which is known to be closely allied to fer- 

 mentation. Ferments and fermentation, as I have already remarked, 

 have very little to do with one another ; and it would save con- 

 fusion and emphasise the fact if we ceased to speak of ferments, but 

 used some of the alternative names which have been proposed for 

 them, such as zymases or enzymes. 



The classical case of fermentation, which is the root of our whole 

 knowledge of the subject, is that of the conversion of sugar into 

 alcohol. Its discovery has everywhere accompanied the first stages 

 of civilisation in the human race. Its details are now taught in our 

 text-books; and I should hardly hope to be excused for referring to 

 it in any detail if it were not necessary for my purpose to draw your 

 attention more particularly to one or two points connected with it. 



Let us trace what happens in a fermenting liquid. It becomes 

 turbid ; it froths and effervesces ; the temperature sensibly increases ; 

 this is the first stage. After this it begins to clear ; the turbidity 

 subsides as a sediment ; the sugar which the fluid at first contained 

 has in great part disappeared, and a new ingredient, alcohol, is 

 found in its place. 



It is just fifty years ago that the great Dutch biologist Schwann 

 made a series of investigations which incontrovertibly demonstrated 

 that both fermentation and putrefaction were due to the presence 

 of minute organisms which live and propagate at the expense of 

 the liquids in which they produce as a result these extraordinary 

 changes. The labours of Pasteur have confirmed Schwann's re- 



sults, and — what could not have been foreseen — have extended the 

 possibilities of this field of investigation to those disturbances in the 

 vital phenomena of living organisms themselves which we include 

 under the name of " disease," and which, no one will dispute, are 

 matters of the deepest concern to every one of us. 



Now, at first sight, the conversion of starch into sugar by means 

 of diastase seems strikingly analogous to the conversion of sugar 

 into alcohol. It is for this reason that the phenomena have been 

 so long associated. But it is easy to show that they are strikingly 

 different. Diastase is a chemical substance of obscure composition, 

 it is true, but inert and destitute of any vital properties, nor is it 

 affected by the changes it induces. Yeast, on the other hand, 

 which is the active agent in alcoholic fermentation, is a definite 

 organism ; it enormously increases during the process, and it 

 appears to me impossible to resist the conclusion that fermentation 

 is a necessary concomitant of the peculiar conditions of its life. 

 Let me give you a few facts which go to prove this. In the first 

 place, you cannot ferment a perfectly pure solution of sugar. The 

 fermentible fluid must contain saline and nitrogenous matters 

 necessary for the nutrition of the yeast protoplasm. In pure sugar 

 the yeast starves. Next, Schwann found that known protoplasmic 

 poisons, by killing the yeast-cells, would prohibit fermentation. 

 He found the same result to hold good of putrefaction, and this 

 is the basis of the whole theory of antiseptics. Nor can the 

 action of yeast be attributed to any ferment which the yeast 

 secretes. It is true that pure cane-sugar cannot be fermented, 

 and that yeast effects the inversion of this, as it is called, into 

 glucose and laevulose. It does this by a ferment which can be 

 extracted from it, and which is often present in plants. But you 

 can extract nothing from yeast which will do its peculiar work 

 apart from itself. Helmholtz made the crucial experiment of sus- 

 pending a bladder full of boiled grape-juice in a vat of fermenting 

 must : it underwent no change ; and even a film of blotting-paper 

 has been found a sufficient obstacle to its action. We are driven, 

 then, necessarily to the conclusion that in the action of "ferments," 

 or zymases, we have to do with a chemical — i.e., a purely physical 

 process ; while in the case of yeast we encounter a purely physio- 

 logical one. 



How, then, is this action to be explained ? Pasteur has laid 

 stress on a fact which had some time been known, that the produc- 

 tion of alcohol from sugar is a result of which yeast has not the 

 monopoly. If ripening fruits, such as plums, are kept in an atmo- 

 sphere free from oxygen, Berard found that they, too, exhibit this 

 remarkable transformation ; their sugar is converted appreciably 

 into alcohol. On the other hand, Pasteur has shown that if yeast 

 is abundantly supplied with oxygen it feeds on the sugar of a fer- 

 mentible fluid without producing alcohol. But under the ordinary 

 circumstances of fermentation its access to oxygen is practically 

 cut off ; the yeast, then, is in exactly the same predicament as the 

 fruit in Berard's experiment. Sugar is broken up into carbon 

 dioxide and alcohol in an amount far in excess of the needs of 

 mere nutrition. In this dissociation it can be shown that an 

 amount of energy is set free in the form of heat equal to about 

 one-tenth of what would be produced by the total combustion of 

 an equivalent amount of grape-sugar. If the protoplasm of the 

 yeast could, with the aid of atmospheric oxygen, completely de- 

 compose a unit of grape-sugar, it would get ten times as much 

 energy in the shape of heat as it could get by breaking it up into 

 alcohol and carbon dioxide. It follows, then, that to do the same 

 amount of growth in either case it must break up ten times as 

 much sugar without a supply of oxygen as with it. And this 

 throws light on what has always been one of themost remarkable facts 

 about fermentation— the enormous amount of change which the 

 yeast manages to effect in proportion to its own development. 



There are still two points about yeast which deserve attention 

 before we dismiss it. When a fermenting liquid comes to contain 

 about 14 per cent, of alcohol the activity of the yeast ceases, quite 

 independently of whether the sugar is used up or not. In other 

 cases of fermentation the same inhibiting effect of the products of 

 fermentation is met with. Thus lactic fermentation soon comes to 

 an end unless calcium carbonate or some similar substance be 

 added, which removes the lactic acid from the solution as fast as it 

 is formed. 



The other point is that in all fermentations, besides what may 

 be termed the primary products of the process, other bodies are 

 produced. In the case of alcoholic fermentation the primary bodies 

 are alcohol and carbon dioxide, the secondary succinic acid and 

 glycerine. Delpino has suggested that these last are residual pro- 

 ducts derived from that portion of the fermentible matter which is 

 directly applied to the nutrition of the protoplasm. 



Yeast, itself the organism which effects the remarkable changes 

 on which I have dwelt, is somewhat of a problem. It is clear 

 that it is a fungus, the germs of which must be ubiquitous frr the 



