54 The Feeding of Animals 



compounds which are included under this term are in 

 part so unlike in chemical and physical properties as to 

 warrant the assertion that they have nothing in com- 

 mon except that they contain nitrogen; and we may 

 believe that their unlikeness in composition is no 

 greater than the differences in their nutritive functions. 



It is very evident that it is not only convenient, but 

 necessary, to classify such a heterogeneous group of bod- 

 ies into subdivisions more nearly alike in their charac- 

 teristics. When we come to consider doing this we 

 discover a most unfortunate confusion of terms. Our 

 leading chemists evidently have reached no agreement 

 in this matter, and so we find almost as many ways of 

 dividing the nitrogenous compounds of plant and ani- 

 mal life as there are prominent writers. 



Nevertheless, some system of classification must be 

 used in this connection, and perhaps none is more con- 

 venient or logical than the one reported by a commit- 

 tee on nomenclature, representing the Association of 

 Agricultural Colleges and Experiment Stations. 



The classification given here is essentially this one, 

 although there a,re included in it certain distinctions 

 very clearly set forth by Professor Atwater in a paper 

 associated with the above-mentioned report. 



In the arrangement adopted it is recognized that 

 certain nitrogen bodies included under protein are so 

 unlike the main and important members of this group 

 as to be properly styled non-proteid. It is also con- 

 ceded that there are simple or native proteids which 

 seem to stand in the relation of "mother" substances 

 to a large number of protein bodies that have been 



