SPECIAL FOKMS OF FOOD. 



93 



abundant supply of proteids would suffice for all nutritive pur- 

 poses, and alone form an adequate diet. Theoretically, proteid 

 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 of 

 numerous experiments show that no group of the food-stuffs al- 

 ready enumerated can alone sustain the body, but rather that a 

 certain proportion of each is absolutely necessary for life. 



Water. 



Bread, 



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

 ical comestibles. The numbers indicate the percentages. Indigestible ma- 

 terials are omitted. 



SPECIAL FORMS OF FOOD. 



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

 cording to the source from which they are derived, It will be 



