PREFACE TO SECOND EDITION 



The kind reception accorded this volume by the instructors in 

 physiological chemistry in the United States and Great Britain has 

 made the preparation of a new edition imperative, notwithstanding 

 the fact that less than two years have elapsed since the former 

 edition appeared. The advance and development made in the field 

 of physiological chemistry during this period have been both rapid 

 and important; conditions which would of themselves have neces- 

 sitated the revision of the volume at an early date. 



The book has been thoroughly revised in all departments and in 

 part rewritten, the system of spelling officially adopted by the 

 American Chemical Society having been followed throughout the 

 volume. Besides introducing many new qualitative tests and quan- 

 titative methods, the author has added a chapter on " Enzymes and 

 Their Action " and has rewritten the two chapters on Proteins. 

 The term " protein " has been substituted for " proteid " and the 

 classification of proteins as recently adopted by the American Physi- 

 ological Society and the American Society of Biological Chemists 

 has been introduced and is followed throughout the text ; the classi- 

 fication adopted by the British Medical Association is also included. 



The original plan of the book has been adhered to with the excep- 

 tion that the chapter on " Enzymes and Their Action " has been 

 made Chapter I and the practical work upon the proteins is pre- 

 ceded by a chapter giving a brief discussion of protein substances 

 from the standpoint of their decomposition and synthesis. We 

 believe that the student will be able to pursue his practical work 

 more intelligently and will derive greater benefit therefrom if the 

 plan of instruction as suggested in Chapters IV and V be followed 

 in the presentation of the subject of " Proteins." 



The author wishes to express his thanks to all those who so kindly 

 offered suggestions for the betterment of the book. He is particu- 

 larly desirous of expressing his gratitude to Professor Lafayette B. 

 Mendel and Dr. Thomas B. Osborne for the many helpful sugges- 

 tions they have so kindly given him. His thanks are also due Pro- 

 fessor C. A. Herter, Dr. H. D. Dakin, Dr. S. R. Benedict and Mr. 

 S. C. Clark for permission to insert unpublished material, to Mr. 

 Paul E. Howe for valuable assistance rendered in the reading of 



vii 



