68 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



Meats: Ox. Calf. Pig. Fowl. Pike. 



Water 76.7 75.6 72.6 70.8 79.3 



Solids 23.3 24.4 27.4 29.2 20.7 



Proteins 20.0 19.4 19-9 22.7 18.3 



Fats 1.5 2.9 6.2 4.1 0.7 



Carbohydrates 0.6 0.8 0.6 1.3 0.9 



Salts 1.2 1.3 i.i i.i 0.8 



Vegetable Foods: Wheat. Barley. Oats. Rice. Peas. Potatoes. 



DIGESTION. 



Object. Digestion is largely a chemical process. Certain 

 physical phenomena are auxiliary. The foods not yielding en- 

 ergy are not affected in a chemical way by digestion. They are 

 simply dissolved, if not already in solution, and are discharged 

 from the body in the same condition in which they entered. But 

 the other classes of food must either be separated from innutri- 

 tious substances with which they enter, or undergo certain 

 changes themselves, or both, before they can be absorbed and 

 assimilated. This necessitates a complicated digestive apparatus 

 and the subjecting of different classes of food to different diges- 

 tive fluids and other gastro-intestinal influences. The object of 

 digestion is therefore twofold, first, to convert the foods into 

 soluble materials and, second, to bring about such changes in 

 their composition as will insure their absorption and appropria- 

 tion by the tissues. 



Enzymes. The chemical changes taking place in digestion 

 are of a peculiar nature, in that they are effected largely by the 

 presence of substances known as enzymes, corresponding in an 



