CHAPTER XXXV 

 Chemistry of Digestion and Nutrition 



449. Digestion, a Biochemical Process. In the diges- 

 tion of food, the enzymes or soluble ferments take an im- 

 portant part. Although digestion is not well understood 

 it is known to be largely a chemical process brought about 

 by ferment action, and hence is called a biochemical pro- 

 cess. The cells in the different parts of the digestive 

 tract secrete chemical products which produce chemical 

 changes in the food, rendering it soluble so that the vari- 

 ous nutrients can be absorbed and used by the body. Any 

 compound which is capable of undergoing digestion and 

 being utilized for food purposes is called a nutrient. The 

 value of any food depends upon the kinds and amounts 

 of nutrients present. During the process of digestion, a 

 complex series of chemical changes take place, and as a 

 result of this process and the assimilation of the food by 

 the body, heat and energy are produced. 



450. Digestion Experiments. The digestibility of a 

 food is determined by a digestion experiment. The per- 

 centage amount of a nutrient which is digested is called 

 the coefficient of digestibility. Not all of the nutrients 

 in foods are alike digestible. In clover hay, for example, 

 65 per cent, of the organic matter is digested, while 

 only 30 per cent, of the crude fiber and 70 per cent, of 

 the nitrogen free extract compounds are digested. Each 

 compound has its own digestion coefficient. In order to 

 determine the digestibility of a food, an animal is fed, for 



