SILOS, ENSILAGE AND SILAGE. 47 



mentation require certain conditions of temperature, 

 moisture and food supply, for the normal exercise of 

 their vital activities ; and each species needs some spe- 

 cial adjustment of these conditions to furnish it the best 

 facilities for carrying on its processes of nutrition and 

 reproduction, and give it the advantage, in the struggle 

 for existence with other species. 



The living organisms of fermentation must not, how- 

 ever, be looked upon as engaged in the direct manufac- 

 ture of some special product that characterizes the kind 

 of fermentation with which they are associated. Beer 

 yeast, for example, is not directly engaged in making 

 alcohol, and the lactic ferment is not directly engaged 

 in making lactic acid, although alcohol and lactic acid 

 are, respectively, the dominant products resulting from 

 the exercise of th?ir physiological activities, when they 

 are provided with the food that is best adapted to their 

 wants. The fermentable materials constitute their food 

 supply, from which they take what is needed for their 

 nutrition, and the resulting residue we recognize as the 

 product of fermentation. 



When beer yeast feeds on sugar it leaves alcohol as a 

 prominent constituent of the residue, which, as a whole, 

 will of course vary with the other materials associated 

 with the sugar ; the lactic ferment feeds on milk, and 

 leaves lactic acid as a characteristic constituent of the 

 residue, and the same may be said of each specific fer- 

 ment, that it appropriates from its food what is needed 

 for its nourishment, and the remains of the feast will 

 vary with the character of the food and the organism 

 that fed upon it. 



The chemical notions of fermentation, the legitimate 

 consequence of Liebig's theory, were, that the saccharine, 

 alcoholic, acetic, lactic, butyric and putrefactive fer- 

 mentations were successive stages of a consecutive series 

 of changes tending to putrefaction as a final result, and 



