358 ELEMENTS OF GENERAL SCIENCE 



but the starchy foods which should have been digested in the 

 mouth, in part at least, add an extra burden to the work of 

 the starch-digesting element of the pancreatic secretion ; even 

 here they may not be thoroughly digested and so may not all 

 be used in the nutrition of the body. One is in no danger 

 of being too thorough in the mastication of his food. 



365. Amount of food. The discussion and food charts pre- 

 sented in section 353 gave definite information regarding the 

 kinds of foods, a list of substances from which different kinds 

 of foods may be secured, and a basis of comparison of the 

 costs of foods from the different substances listed. Since 

 the digestive system is so organized that it can digest car- 

 bohydrates, fats, and proteins, and since all these are needed 

 for proper nutrition, it is of much hygienic importance that 

 these foods be used in as nearly proper proportion as can 

 be arranged. If a person eats but one kind of food he is 

 not properly nourished, and the work of digestion is not 

 distributed to the whole digestive system. The appetite may 

 serve as a partial guide to the kind of food needed, but it 

 is not fully to be trusted, partly because we are often uncer- 

 tain concerning the exact kind of food we are hungry for and 

 partly because our habits of eating often cultivate appetites 

 that may not call for exactly what we need. 



Experiments have been performed in the effort to deter- 

 mine what amounts of food are necessary for persons engaged 

 in active work. It is stated roughly that active workers 

 require from 100 to 125 grams of protein food per day; 

 but it has also been shown that such workers as soldiers, 

 teachers, and athletes may work effectively for at least several 

 months upon less protein food ; that is, from 40 to 50 grams 

 per day. Similarly, it has been stated that a representative 

 distribution of foods for the composition of an ordinary 

 day's diet may consist of protein, 118 grams; fats, 56 grams; 

 carbohydrates, 500 grams. It must be kept in mind, how- 

 ever, that the above figures are merely suggestive. So much 



