April 21, 1898] 



NA TURE 



593 



This explanation seemed to apply to all fermentations be- 

 sides the alcoholic one, and was for that reason favourably 

 received by many ; some, indeed, thinking that all fermentations 

 were fundamentally alike, and that the different products were 

 due to the degree of the alteration ofthe decomposing substance. 



This view led to the idea that the action of the yeast was 

 not due to its vital processes, but rather to a decomposition of 

 its proteid constituents regarded simply as nitrogenous sub- 

 stance. 



A third hypothesis was advanced by Berzelius, who thought 

 that fermentation is a contact action due to a catalytic force. 

 This idea has met with very little support. 



Pasteur's biological explanation of the action of yeast 

 gradually made itself accepted, even to a certain extent modi- 

 fying Liebig's position. The latter chemist, in his later 

 writings, while adhering to his theory of a molecular vibration, 

 insists that it is not antagonistic to Pasteur's views, but that 

 the movement is set up by the organisms in the course of their 

 vital activity. 



The dependence of alcoholic fermentation on the presence of 

 yeast in a living and active condition seemed, so far as the 

 earlier observers went, to be absolute, and the power of the 

 organism to bring it about appeared to indicate a special 

 property of the yeast cell. The question, however, was soon 

 raised whether or no this property was shared by other or- 

 ganisms than this simple one ; whether, in fact, it was not 

 rather a manifestation of certain powers of vegetable protoplasm 

 when placed under abnormal conditions. Reasons for holding 

 the latter view were soon forthcoming. 



In 1869 MM. Lechartier and Bellamy published an account 

 of some experiments made with ripe fruits, which they kept 

 for several months in the absence of oxygen. They found that 

 under these conditions the fruits gave off continuously a certain 

 quantity of CO,, and that at the end of the experiment the 

 pulp contained a measurable quantity of alcohol. Microscopic 

 examination of the pulp showed it to be free from any yeast 

 cells. These observations were shortly afterwards confirmed 

 by Pasteur. 



In speculating as to the part which these fermentative pro- 

 cesses play in the life of the vegetable cell, Pasteur came to the 

 conclusion that the fermentative power was connected with 

 nutrition in the absepce of free oxygen, and that the effort to 

 obtain oxygen under these conditions led to the decomposition 

 of the sugar. He strengthened himself in this opinion by ex- 

 periments on the cultivation of yeast in the absence of free 

 oxygen, carried on side by side with others in which the gas 

 was supplied freely to the organism. In these experiments he 

 found that the relative weights of yeast formed and sugar de- 

 composed were very different under the two conditions. When 

 no oxygen was supplied, fermentation was very slow, and for one 

 part of yeast formed 60 to 80 parts of sugar disappeared. When 

 oxygen was admitted the fermentation was very rapid, but for 

 one part of yeast formed not more than 4 to 10 parts of sugar 

 were decomposed. This difference was not due to any weaken- 

 ing of the energy of the yeast in the second case, for when some 

 of it was removed and made to act on sugar in the absence of 

 oxygen, it behaved just as did that which was used in the first 

 experiment. 



In this way Pasteur was led to hold that fermentation is a 

 kind of intra-molecular respiration, a view which, however, was 

 not allowed to pass without challenge. 



Schiitzenberger argues against it with some force, pointing 

 out at the outset that there ^eems to be a contradiction between 

 the facts and Pasteur's inferences. In the presence of free 

 oxygen we have a very active fermentation set up, while the 

 yeast is said to possess less fermentative power. Schiitzenberger 

 claims that the fermentative power is not the same thing as the 

 power of growth, nutrition, and multiplication ; that it is a 

 distinct quality which exists in the yeast cells so long as they 

 are living, but is not directly related to the respiratory process. 



He bases his view on experiments carried out to ascertain how 

 respiration is affected under changed conditions. The results he 

 obtained were briefly the following : — 



(i) Ina watery liquid without sugar, but containing oxygen 

 in solution, the quantity of oxygen absorbed in unit time by a 

 gramme of yeast is constant, whatever proportion of oxygen is 

 present. 



(2) In a saccharine liquid, containing also albuminous matter, 

 and with oxygen in solution, the same result is obtained, except 

 that the quantity absorbed in unit time is greater. 



NO. i486, VOL. 57] 



(3) In two digestions, carried on side by side for some time, 

 one being supplied continuously with oxygen and the other 

 deprived of it, the former produced most alcohol. 



If the decomposition of the sugar had been the result of the 

 respiratory activity of the yeast cells at the expense of the com- 

 bined oxygen of the sugar, it would seem that fermentation 

 should either not have taken place at all in the presence of free 

 oxygen, or that it should have been much less than in the other 

 case, whereas the reverse is what is found. 



Hence, Schiitzenberger comes to the conclusion that the 

 sugar is alimentary and not respiratory. 



Pasteur's theory has also found a powerful opponent in 

 Naegeli, who held views much like those advanced by Liebig, 

 Willis and Stahl. He thought that the decomposition of the 

 sugar is brought about by vibrations of the plasma molecules, 

 transferred to the fermentable substance, and that it takes 

 place to a small extent only inside the cells, but to a much 

 greater one in the liquid outside them. 



A great development of our knowledge of the details of 

 fermentation has taken place during the last twenty years, due 

 in large measure to the labours of Hansen. Prior to 1878 

 much uncertainty prevailed concerning the true Saccharomy- 

 cetes. By most laborious and careful cultivation, an ac- 

 quaintance has been made by him with the life-history and 

 mode of behaviour under various conditions of six definite 

 species of these fungi. Other investigators have described other 

 species, and a copious literature has sprung up on the subject. 



Another fact of importance has also been ascertained 

 which explains the discrepancies of analysis observed so long 

 ago by Gay-Lussac, Dumas and others. It was mentioned 

 above, that the composition of the fermented sugar as com- 

 puted from the measurement of the COj and alcohol it 

 furnished, must be expressed by the lormula CgHjaOg, 

 while the analysis of cane-sugar showed it to be Ci-jHa^Oii. 

 Dumas suggested that it took up water during the alcoholic 

 fermentation. It is now known that this hydrolysis takes 

 place before such a fermentation begins, and that it is set 

 up by a special enzyme which can be extracted from yeast. If 

 a watery extract be made of yeast pressed till nearly or quite 

 dry, the cells give up to the solvent a body which has been 

 called invertin or invertase. When a liquid containing this 

 is added to a solution of cane-sugar, the latter is found to be 

 very rapidly split up according to the equation 



CiaHasOn -f H2O = <Z^\l^^O^ -f- QllioOg.! 



Two sugars are formed, one of which rotates a beam of 

 polarised light to the right, the other to the left. These, which 

 were on this account termed dextrose and levulose respectively, 

 are now known as glucose and fructose. These two sugars are 

 those which undergo the alcoholic fermentation, while the cane- 

 sugar itself is incapable of so behaving. The extract of the 

 yeast can carry out the hydrolysis without the cells themselves 

 being present. 



More recently still, the sugar maltose, which is the product 

 formed by the action of diastase on starch, and which is 

 consequently always present in malted grain, has been ascer- 

 tained to undergo a similar hydrolysis to cane-sugar, but to 

 yield two molecules of glucose in consequence. The enzyme 

 which causes this hydrolysis is also present in the malt. It is 

 called by some writers glucase, by others maltase. 



Fischer states that such an hydrolysis is necessary in the case 

 of all polysaccharides, or sugars with the empirical formula 

 C12H22OJ1. Thus the sugars which are immediately capable of 

 giving rise to alcohol are especially glucose and fructose ; 

 those which are commonly found in the liquids which are 

 fermentable being, in addition, cane-sugar and maltose. The 

 latter always undergo conversion or hydrolysis, and form one or 

 both of the former. 



The course of action on mixtures of these sugars in the pre- 

 sence of different species of yeast is often very different. Thus 

 Hansen's six true species of Saccharomycetes all hydrolyse 

 both cane-sugar and maltose, besides carrying on alcoholic 

 fermentation of their products. ^. Marxiamts differs in not 

 attacking maltose, while S. niembramefacieiis ferments none of 

 them, and does not contain invertase. Other organisms have 

 similar idiosyncrasies. 



Fischer advances a hypothesis to explain this great variety of 

 action, which throws a great deal of light on the subject. Re- 

 cognising, as it is now possible to do, that different sugars have 

 different molecular configurations, he suggests that the ferment- 



