CHEMICAL COMPOSITION OF THE BODY 29 



hence it follows that proteids form an absolutely necessary 

 part of our food. We must eat a sufficient amount of 

 proteid or we shall starve, no matter how much other food 

 we eat. Proteid is needed in all the working parts of the 

 body. Muscle and blood are pre-eminently active. Perform- 

 ing absolutely vital functions every moment of our lives, 

 they are constantly exposed to "wear and tear" and unless 

 they were repaired would become exhausted and worn out. 

 The body must have new proteid for repair purposes and the 

 proteid must be provided by the use of proteid-containing food. 

 This food may be obtained from many sources. Some 

 proteids come from animal and some from vegetable materials. 

 That from meats is called myo&in; that from eggs is albumen] 

 that from milk is casein] that from wheat is gluten] that 

 from beans is legumen. But although differently named and 

 differing in value to the body, all these forms of proteid serve 

 as a food which can replace and repair the worn-out parts of 

 the body. If we remember that proteids alone can thus re- 

 place worn-out tissue, we shall understand their fundamental 

 importance. 



One naturally and correctly feels that proteids from animal 

 sources are probably most like that of the human body, and 

 so can be used with better results. Furthermore, as all sub- 

 stances taken as foods must be masticated, swallowed, digested, 

 absorbed into the blood, carried over the body and then re- 

 ceived into the living cells and made a part of the body sub- 

 stance, it is easy to imagine that some proteids undergo these 

 changes more readily than others, and so are more valuable. 



In a later chapter dealing with foods the differing values 

 of various proteids will be discussed. Some kinds, taken 

 alone, will not support the growth of an animal at all; others 

 seem to furnish every needed substance, even when quite 

 small quantities are taken. Very extensive and expensive 

 studies have been made in recent years in the analysis of all 

 kinds of proteids and other food substances, together with 



