X PREFACE TO FIRST EDITION. 



biochemic substances. The micro-photograph of allantoin was 

 kindly furnished by Professor Mendel. The author is also indebted 

 for suggestions and assistance received from the lectures and pub- 

 lished writings of numerous authors and investigators. 



The original drawings of the volume were made by Mr. Louis 

 Schmidt whose eminently satisfactory efforts are highly appreciated 

 by the author. 



PHILIP B. HAWK. 



PHILADELPHIA. 



