THE DIGESTION OF FOOD 119 



The physical condition of the feces is characteristic 

 with each species of animals, the differences in consistency 

 being due largely to variations in the amount of water 

 present. The amount of water in feces depends more 

 upon the character of the food eaten than upon the 

 amount of water drunk. 



THE KELATION OF THE DIFFERENT FOOD COMPOUNDS TO 

 THE DIGESTIVE PEOCESSES 



Numerous digestion experiments with a large variety 

 of foods have abundantly established the fact that these 

 materials differ greatly in their solubility in the digestive 

 juices. This is an important matter, and one which should 

 be well understood, for we must consider both the weight 

 of the dry matter eaten and its availability in determin- 

 ing its nutritive value. Variations in digestibility are 

 caused primarily by variations in composition; therefore, 

 we must deal fundamentally with the susceptibility of the 

 various single constituents of food to the action of the 

 several digestive ferments. 



In this connection, we need to pay little attention to 

 the mineral compounds that exist in the inorganic form 

 in the food. They do not undergo fermentative changes 

 in the way that the carbon compoimds do, but are brought 

 into simple solution either in the water accompanying the 

 food, or in the juices with which they come in contact. 



175. Digestibility of the proteins. — ^As has been noted, 

 protein is a mixtiu-e of nitrogenous compounds. The gluten 

 of wheat contains at least five of these bodies, and other 

 seeds as many. What is the relative susceptibility of these 

 single proteins to the digestive enzyms either as to rapid- 

 ity or completeness of change does not appear to be known. 



