PREFACE vii 



students who are preparing for advanced work in agricultural 

 science, in animal or human nutrition, etc. 



An attempt has been made to arrange the material in such a 

 way as to proceed from simpler chemical principles and sub- 

 stances to those of more complex structures. This results in an 

 arrangement of the groups to be studied in an order which is quite 

 different than their biological significance might suggest. It is 

 believed, however, that in the end a more systematic under- 

 standing and a more orderly procedure is obtained in this way 

 than would result from the treatment of the groups in the order 

 of their relative biological importance. 



