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LECTURE XVII 



FERMENTATION 



The destructive metabolism which is an essential concomitant of vitality 

 in so far as it consists in the complete combustion of organic materials with 

 the production of carbon-dioxide and water, we have termed respiration. In 

 the present lecture we propose to treat of fermentation, by which we mean 

 an active metabolism where the oxidation is incomplete or where, instead of 

 oxidation, a decomposition of an entirely different kind takes place. Respiration 

 and fermentation have in common the formation of final products having less 

 heat of combustion and more limited stores of energy than the materials from which 

 they arise. In the formation of these final products energy must therefore be 

 released, and it is this energy which the organism makes use of in some unknown 

 way to carry out its vital activities. As has been shown in the last lecture, respira- 

 tion and fermentation are not two essentially different processes, for since we 

 found that in the respiration of Fungi, for example, a number of organic acids, 

 such as oxalic, malic, &c . , arose as products of incomplete combustion, we are quite 

 entitled to term this process fermentation, and speak of oxalic acid fermenta- 

 tion, malic acid fermentation, and so on, after the chief products produced. 

 The nomenclature of fermentation is not as yet quite consistent since it is some- 

 times basedon the natureof the chief, or to be more accurate, the most noticeable, 

 product — for in alcoholic fermentation carbon-dioxide is as much the chief 

 product as alcohol is — sometimes also after the material that is fermented. Thus 

 by butyric acid fermentation one understands a process in which butyric acid 

 is the most prominent product which arises, but by cellulose-fermentation we 

 mean a process which results in the destruction of cellulose. As an example 

 of another type of fermentation which takes place without the presence of 

 oxygen, may be taken that in which alcohol is formed as a result of intra-mole- 

 cular respiration. We have already established the fact that this alcoholic 

 fermentation stands partly, at least, in lieu of respiration ; so long as intra- 

 molecular respiration continues, the plants we have hitherto been considering 

 cannot develop their full vital capacities — their growth, for example, comes to 

 a standstill — but still they remain alive and regain their ordinary powers after 

 being transferred to normal conditions and after the addition of oxygen. If, 

 however, one places these organisms in an atmosphere free of oxygen — which 

 may be easily done in the case of Fungi — without at the same time permitting 

 the conditions necessary for the formation of alcohol, and if one gives them in 

 place of an easily fermentable sugar another equally nutritive source of carbon, 

 e. g. quinic acid, lactose (Diakonow, 1886), they rapidly die. [Diakonow's 

 work has not, however, received complete confirmation, for Nabokich (1903) 

 and KosTYTSCHEW (1904) have shown that peptone, quinic acid, and milk- 

 sugar may also support intra-molecular respiration, but nothing like so well as 

 sugar.] Similarly, oily seeds cannot respire intra-molecularly so well as 

 starchy seeds (Maze, 1900; Godlewski, 1901) because the alteration of fat into 

 carbohydrate is manifestly impossible without oxygen. There is no ground for 

 distinguishing the process of alcohol formation which takes place in intra- 

 molecular respiration from alcoholic fermentation so called, especially since 

 Godlewski has demonstrated that alcohol and carbon-dioxide occur in the same 

 proportions as in fermentation, and that they also develop in seedlings of Pha- 

 nerogams from sugar supplied artificially. Still the term 'alcoholic fermenta- 

 tion ' always suggests in the first instance a definite organism, viz. yeast, because 



