PREFACE TO THIRD EDITION. 



WORK upon the chemistry of the proteins is always in progress, 

 and a large amount of new matter has required incorporation 

 in this edition. At the same time a thorough revision has been 

 made, and the former omission of references in the text to the 

 papers quoted in the bibliography has been remedied. 



The new matter in this edition is mainly connected with the 

 analysis of proteins. It has therefore been thought advantage- 

 ous to divide this part of the monograph into two : Part I. 

 Analysis. Part II. The Amino Acids. New or improved 

 analytical methods are constantly being devised, whilst the 

 description of the amino acids is a more definite part of the 

 subject matter. 



The division into two parts will be a saving of labour to 

 author, publisher and printer, and the expense to the purchaser 

 will be lessened. The editors mentioned these considerations 

 at the time the monographs were first issued. 



R. H. A. P. 



April, 1917. 



