140 THE BODY AT WORK 



continuously masticate nuts and biscuits. Thirdly, the meal 

 must not be so large that the stomach cannot deal with it 

 " at a sitting." In from two to three hours the last of the . 

 food should have passed through the pylorus, allowing the 1 

 stomach to rest before it is called into activity again. As 1 

 proteins are practically the only foods which are digested in 7 

 the stomach, the work required of this organ depends upon / 

 the quantity of proteins present amongst the constituents / 

 of a meal. Meat is the food richest in proteins, although/ 

 bread, vegetables, milk, cheese also yield them. Some people 

 can digest three meat meals every day ; but others, probably 

 the majority, find that it is unwise to take any considerable 

 quantity of meat more than once in twenty-four hours. It is 

 only when the cells of the gastric glands have accumulated a 

 store of pepsinogen-granules that proteid digestion is vigorously 

 carried on. Fourthly, the food must be in a form in which 

 it does not irritate the stomach, provoking an outflow of acid 

 out of proportion to the pepsin which accompanies it. Ex- 

 perience alone can teach the foods which are to be avoided on 

 this account. But speaking generally, it may be said that the 

 stomach resents the presence of substances which cannot be 

 amalgamated into chyme. Its task is the reduction of the 

 mixture of foods which compose a meal to the consistence of 

 a smooth cream. Hot buttered toast or pie-crust are made 

 of wholesome constituents enough, but, fat being melted into 

 the starch, the fragments are impermeable to the gastric juice. 

 They act mechanically as irritants of the mucous membrane. 

 Again, it may be said that " pure " foods are apt to provoke 

 acidity. Nothing could be more wholesome than eggs or 

 pounded meat or custard pudding ; but taken by themselves 

 these articles of diet over-stimulate the mucous membrane. 

 They need to be diluted with starch-foods, or even with 

 cellulose. 



And this calls attention to the dietetic value of vegetables. 

 Vegetables, which consist chiefly of innutritious cellulose, 

 distribute the digestible constituents of a meal and increase 

 its bulk, greatly favouring its progress through the alimentary 

 canal. Especially in herbivora is it important that the bulk 

 and looseness of the food should be well maintained. Rabbits \ 

 thrive on sugar, starch, and albumin, mixed with such an 



