Vlll PREFACE TO SECOND EDITION. 



proof and in the verification of tests and methods, and to Dr. M. E. 

 Rehfuss for assistance in proof reading. 



The author takes this opportunity of making an acknowledg- 

 ment which was inadvertently omitted from the first edition. He 

 wishes to express his obligation to the laboratories of physiological 

 chemistry at Yale University and at Columbia University (College 

 of Physicians and Surgeons) in the latter of which he was Assistant 

 to Professor W. J. Gies for two years. The courses given in these 

 laboratories formed the basis of many of the experiments included 

 in this volume and it is with feelings of deepest gratitude that he 

 records this acknowledgment of the assistance thus rendered by 

 those in charge of these courses. 



PHILIP B. HAWK. 



URBANA, ILLINOIS, 

 February I, 1909. 



