THE NITROGEN COMPOUNDS 



51 



roots, such as beets and turnips, contain more nitrogen 

 in the non-protein form. Proteins are the chief constit- 

 uents of muscular tissue. Their chemical constitution is 

 not definitely known, but it is generally considered 

 to be very complex, even to the extent of several 

 thousand atoms. These bodies are constructed from 

 the simpler ones of the inorganic world through the 

 vital energies of plants, and in order to serve the 

 purposes of nutrition they must come to the animal fully 

 organized. 



64. Ultimate composition of proteins. — ^The ultimate 

 composition of proteins, that is, the proportions of the 

 elements which they contain, has been carefully studied, 

 and while there are material differences among them in 

 this respect, the limits of variation are not especially 

 wide, as can be seen from the following figures according 

 to Osborne:* 



* "Chemistry of Food and Nutrition," Sherman, page 35. 



