xii ACKNOWLEDGMENTS 



The following have read the manuscripts either com- 

 pletely or in part and have given valuable constructive 

 criticisms : Edith H. Bourne, the Fannie H. Smith Train- 

 ing School, Bridgeport, Connecticut ; Francis R. Hunter, 

 Assistant in Biology, Princeton University; George W. 

 Hunter, III, Assistant Professor of Biology, Wesleyan Uni- 

 versity ; Roy A. Knapp, Principal Antelope Valley Joint 

 Union High School, Lancaster, California; and Frank 

 M. Wheat, Chairman of Department of Biology, George 

 Washington High School. In addition Dr. Wheat has 

 added much to the teaching effectiveness of these books 

 by his excellent diagrams and skillful cartoons. Wright 

 Pierce has also added much to the attractiveness of the 

 text with his illuminating photographs. Professor Francis 

 B. Sumner has kindly allowed the use of photographs from 

 an original experiment. Miss Florence E. Wall, F.A.I.C., 

 has given valuable suggestions on the hygiene of the skin. 

 Dean Collins P. Bliss of the School of Engineering of New 

 York University has offered much technical advice in 

 certain parts of the text. To all of the above is given the 

 sincere thanks of the authors. 



