92 THE FEEDING OF ANIMALS 



among the most useful agencies with which we deal and 

 some are harmful. The yeast plant is useful in bread- 

 making, but the putrefaction of meats under the influence 

 of another ferment causes loss. 



127. Bacteria in the digestive tract. — The digestive 

 tract of animals is inhabited by countless numbers of 

 bacteria. These inhabit both the stomach and the intes- 

 tines, especially the colon. They also form a part of the 

 feces. The two main types in which we are interested in 

 their relation to digestion are (1) the fermentative or those 

 that attack the carbohydrates, especially the sugars, and 

 (2) the putrefactive, or those that cause decomposition of 

 the proteins. Under certain conditions such as a sudden 

 change of food to large amounts of young and succulent 

 herbage, especially the legumes, bacterial fermentations 

 may endanger the life of the animal through the exces- 

 sive formation of acids and gases. 



128. Unorganized ferments. — ^There is another class of 

 ferments which is termed imorganized, and to which the 

 general term "enzym" is given. These are the ferments 

 especially important in digestion. They are merely chemi- 

 cal compounds, formed within the living cells of the 

 plant or animal, which produce a peculiar effect upon 

 certain bodies with which they come in contact. If a 

 thin piece of lean beef be suspended in an extract from 

 the mucous lining of a pig's stomach, to which has been 

 added a small proportion of hydrochloric acid, the liquid 

 being kept at about 98° F., the beef will soon begin to 

 soften, afterwards swell to a more or less jelly-like con- 

 dition, and finally dissolve. The same general result 

 would occur with fish, blood fibrin, or the coagulated 

 white of an egg. When starch is placed in a warm-water 

 solution of crushed malt, it soon dissolves, leaving a com- 



