102 



MANUAL OF PHYSIOLOGY. 



alone ought to be sufficient for nutrition. It, however, has been 

 frequently tested by experiment, and practically decided, that an 

 animal will not thrive upon a free supply of pure proteid food 

 alone ; and in the human subject such exclusive diet would induce 

 dangerous abnormal conditions in a short time. Since nitrogen 

 is an important element in nearly all parts of the body, we could 

 hardly expect that a diet composed of non- nitrogenous food stuffs 

 alone could support the animal economy. In short, the results 



Proteids. 



FIG. 42. 



Fats. Carbohydrates. 



Water. 



Human milk, 



Cow's milk, 



Hi 



P6 





20 



Meat, 



Fish, 



Leguminous fruits, 



Potatoes, 



Green vegetables, . 



Bread, 



Diagram showing the percentage of the principal food stuffs in a few typical comes- 

 tibles. The numbers indicate the percentages. Indigestible materials are omitted. 



of numerous experiments show that no group of the food stuffs 

 already enumerated can alone sustain the body, but rather that 

 a certain proportion of each is absolutely necessary for life. 



SPECIAL FORMS OF FOOD. 



The articles of diet we make use of are animal or vegetable, 

 according to the source from which they are derived. It will be 

 seen that a varying quantity of all chemical classes of food 



