THE DIGESTION OF FOOD 91 



125. Results of fermentation. — ^Like all life, these 

 organisms must have food. Many species find this in 

 acceptable forms in vegetable and animal products. 

 Because these products contain the sugar, proteins, and 

 mineral compounds which nourish bacteria, many of 

 them are the prey of ferments under proper conditions of 

 moisture and temperature. The prevention of fermenta- 

 tion in cattle foods is desirable because it occasions a loss 

 of nutritive value and often produces undesirable flavors. 

 The loss becomes evident when we consider the nature of 

 the chemical changes that occur. For instance, when the 

 sugars in cider are broken up through the influence of a 

 bacterium, carbon dioxid and alcohol are formed through 

 the appropriation of free oxygen. This means that com- 

 bustion occurs, causing the liberation of energy which 

 otherwise would have been available if the sugar had 

 been taken as food. Many other fermentations involve 

 oxidation, all of which are destructive of food value. 



126. Manner of action of ferments. — ^These little 

 plants use sugar and other compounds as food, deriving 

 energy and growth therefrom, the carbonic acid, alcohol, 

 and other new bodies being the by-products of this use. 

 It now appears probable that these organisms develop an 

 unorganized ferment which brings about these fermen- 

 tative changes. Indeed, it is definitely proved that it is 

 possible to separate from the cells of the yeast plant a 

 substance that, in the absence of the yeast plant itself, 

 converts sugar into carbon dioxid and alcohol. This 

 shows that the effective agent in bacterial fermentations 

 is, after all, a chemical substance, or an unorganized 

 ferment. These later discoveries tend to remove the dis- 

 tinction that has been made between the so-called organ- 

 ized and unorganized ferments. Certain ferments are 



