8 INTKODUCTION. 



These investigations are of more than usual interest, because they 

 expand the ideas which have heretofore been held respecting the 

 application of agricultural chemistry. To many people agricultural 

 chemistry means solely the analyses of soils and fertilizers, whereas 

 in its broadest sense it covers the study of the composition of plants 

 and animals and the foods which produce them. Agricultural 

 chemistry in this sense becomes one of the most important of the 

 biological sciences, and as such is now recognized by those who fully 

 understand its scope and its possibilities. 



H. W. WILEY, 

 Chief of Bureau. 



