THE NITROGEN COMPOUNDS 49 



number of cereal grains and leguminous seeds, 5.5 for 

 the oil and lupine seeds, and 6 for barley, maize, buck- 

 wheat, soja-bean, and white bean (Phaseolus), rape and 

 other brassicas. Nothing short of inability to secure 

 greater accuracy justifies the longer continuance of a 

 method of calculation which is apparently so greatly 

 erroneous. 



61. So-called proteins greatly unlike. — ^As previously 

 stated, protein is the accepted name for a class of com- 

 pounds. Just how there came about such a grouping 

 of a large number of substances imder a single head it is 

 not necessary to consider in this connection, but it should 

 be made clear that the individual compounds which are 

 included imder this term are greatly imlike in their 

 chemical and physical properties; and it is known that 

 they differ materially in their nutritive functions. 



62. Classification of proteins. — It is very evident that 

 it is not only convenient, but necessary, to classify such 

 a heterogeneous group of bodies into subdivisions more 

 nearly alike in their characteristics. 



The most recent classification is one recommended by 

 committees representing certain scientific bodies.* Doubt- 

 less this classification is only temporary and will be 

 modified as our knowledge of the compounds of nutrition 

 is enlarged. The grouping now agreed upon is based on 

 chemical constitution; at the same time the lines of cleav- 

 age appear to have reference to nutritive function. As will 

 be noticed later, other bodies are related to metabolism 

 and growth which it is not now possible to classify as 

 they have not yet been isolated and their chemical con- 

 stitution is undetermined. The terms used in this classi- 

 fication are explained in the text which follows: 



*Ain. Jour. Phys., Vol. XXI. 



