292 , BOAED OF AGRICULTURE. 



of what is required in the nutritive functions of the bacteria 

 that produce it. 



In advocating these views Pasteur says : " Originally, 

 when fermentations were put amongst the class of decompo- 

 sitions by contact-action, it seemed probable, and, in fact, 

 was actually believed, that every fermentation had its own 

 well-developed equation, which never varied. 



" In the present day, on the contrary, it must be borne in 

 mind that the equation of a fermentation varies essentially 

 with the conditions under which that fermentation is accomp- 

 lished, and that a statement of this equation is a problem no 

 less complicated than that in the case of the nutrition of a 

 living being. To every fermentation may be assigned an 

 equation in a general sort of way, — an equation, however, 

 which in numerous points of detail is liable to the thousand 

 variations connected with the phenomena of life. More- 

 over, there will be as many distinct fermentations brought 

 about by one ferment as there are fermentable substances 

 capable of supplying the carbon element of the food of that 

 same ferment, in the same way that the equation of the 

 nutrition of an animal will vary with the nature of the food 

 which it consumes. As regards fermentation producing 

 alcohol, which may be effected by several different ferments, 

 there will be, in the case of a given sugar, as many general 

 equations as there are ferments, whether they be ferment- 

 cells, properly so called, or cells of the organs of living 

 beings functioning as ferments. In the same way the equa- 

 tion of nutrition varies in the case of different animals nour- 

 ished on the same food. These remarks are applicable to all 

 ferments alike ; for instance, butyric ferment is capable of 

 producing a host of distinct fermentations, in consequence 

 of its ability to derive the carbonaceous part of its food 

 from very different substances, from sugar, or lactic acid, or 

 glycerine, or mannite, and many others. Moreover, it is 

 quite erroneous to suppose that the presence of a single one 

 of the products of a fermentation implies the co-existence of a 

 particular ferment. If, for example, we tind alcohol among 

 the products of a fermentation, or even alcohol and carbonic 

 acid gas together, this does not prove that the ferment must 

 be an alcoholic ferment, belonging to alcoholic fermentations 



