380 AGRICULTURAL CHEMISTRY 



work of the digestive tract being termed digestible, while 

 those which require a larger amount of work are said to 

 be indigestible. Some confusion has arisen from this use 

 of the term digestible. For example, rice is frequently 

 called a digestible food and cheese an indigestible food. 

 Digestion experiments have shown that cheese is more 

 completely digested than rice. A food which is easily 

 digested is not necessarily completely digested. 



Individuality influences the digestibility of foods to a 

 marked extent. For example, digestion experiments 

 have shown a difference of over 14 per cent, in diges- 

 tibility of the protein in a mixed ration composed of 

 bread, milk and beans. There is a greater difference 

 between individuals as to the ease of digestion than as to 

 the completeness. Since digestion is largely a biochemical 

 process, its completeness is necessarily influenced by 

 the activity of the cells in the digestive tract. The com- 

 bining of foods influences digestibility. For example, 

 milk in a ration exerts a favorable influence upon the di- 

 gestibility of the other foods with which it is combined. 

 This is because of the presence in milk of enzymes or 

 soluble ferments. Experiments have shown that 12.5 

 per cent, of the protein in a sterile food, as toast, is capa- 

 ble of being digested by the soluble ferments of milk. 



The method of cooking and preparing foods also exerts 

 an influence upon their digestibility. Cooking changes 

 both the physical and chemical composition of foods. 

 The cell walls of vegetables and cereals are broken and 

 the starch granules ruptured, thus exposing them to 

 more thorough action of the digestive fluids. Cooking 



