PREFACE 



During the past few years the physiology of the 

 amino acids has been subjected to much experimenta- 

 tion with the result that these protein cleavage prod- 

 ucts have assumed an ever increasing importance in 

 the problems associated with nitrogenous metabolism. 

 Owing largely to our too recent appreciation of the 

 significance of these substances in metabolic processes 

 there exists at present no compilation which fur- 

 nishes an adequate conception of the roles which may 

 be played by the amino acids. It has been, therefore, 

 the aim of the writer to gather together in one place 

 the results which have thus far been obtained in the 

 field of the biochemistry of the amino acids, thus 

 affording the busy practitioner, and others whose 

 resources for consulting original communications are 

 limited, an opportunity of gaining a knowledge of the 

 present-day problems in this field of nutrition. In the 

 accomplishment of this purpose the writer has made 

 no effort to include all the details or all the literature 

 available upon a given topic, but has sought rather to 

 indicate leading lines of thought. At the end of each 

 chapter are given references in which all the impor- 

 tant literature upon the topic discussed is cited. 



It is assumed that the reader is familiar with the 

 fundamental principles of metabolism, hence, in gen- 

 eral, these have been omitted. 



The author is deeply indebted to Professor Lafay- 

 ette B. Mendel for suggestions, criticisms of the 

 manuscript and for some of the plates presented. 



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