162 Dr. H. Karsten on the Theory 



Probably Liebig would not have taken all these circuitous 

 ways towards the natural explanation of the process of fermen- 

 tation had he known that the yeast-cells, even though they 

 do not increase (nay, perhaps may diminish) in weight, are 

 yet constantly vitally active and engaged in continual new 

 formation, and that during the growth of their membranes 

 these finally become changed into vegetable acids, lactic acid, 

 succinic acid*, and, if we may judge by the analogy of other 

 processes, into glycerine, alcohol, carbonic acid, fat, &c. 



Pasteur, who has so thoroughly studied the chemical pro- 

 ducts of alcoholic fermentation, and so greatly increased our 

 knowledge of them, and to whom we are indebted for finally 

 setting free his confreres from the long persistent error that 

 fermentation is a purely chemical act — even Pasteur, in his 

 fresh attempt to establish a theory of the process of fermenta- 

 tion (' Comptes liendus,' 1872), struck upon the same rock, in 

 thinking that the chemical processes of fermentation differ 

 from a number of other phenomena, and especially from the 

 actions of the other vital phenomena, by the circumstance that 

 a much greater weight of the fermentescible substance is de- 

 composed than the weight of the acting ferment amounts to. 

 That this vieAv is erroneous in every respect we see at once if 

 we compare the quantity of nutriment of any animal with the 

 weight of its body, and, on the other hand, consider the con- 

 tinual regeneration of the yeast-cells, which was urged against 

 Liebig in my ' Beitrag zur Geschichte der Botanik ' (1870). 



Pasteur also believes that this fact of the inferiority of weight 

 of the organized ferment is connected with its nourishment in 

 the absence of free oxygen ; and he finds in this the distinguish- 

 ing characteristic of fermentation as compared with other vital 

 processes. " Fermentation," says Pasteur, " is a special case 

 of a very general phenomenon ; nay, we might say that all 

 creatures, under certain conditions, are ferments. If we kill 

 any creature, or organ in any creature, or a group of cells in 

 this organ, by sufibcation, by cutting through nerves, &c., the 

 physical and chemical life in them will not immediately cease, 

 it will continue ; and when this takes place under such condi- 

 tions that free oxygen (interior or exterior) is wanting, then 

 the organism, the organ, or the cells will necessarily derive 

 the heat which they require for their processes of nourishment 

 and growth from the substances surrounding them ; they will 

 consequently decompose these, and we shall see the peculiar 

 character of fermentations appear, when the amount of heat 

 developed represents the decomposition of a quantity of fer- 



* ' Harz-, Alkohol- und Milclisauregahrimg,' 1871, p. 70, from the * Zeit- 

 8chr. des oesterreich. Apotheke-Vereiues/ 1870-71. 



