Preface vii 



necessary to an intelligent approach to those fields. 

 Most of the techniques described are those de- 

 veloped and perfected in my own laboratory, but 

 I have tried also to provide a working outline of 

 other techniques and methods of approach. 



One does not prepare a book, even a small one, 

 alone. I should like especially to acknowledge 

 the help of Professor Edmund Sinnott of Yale, 

 Professor George Avery and Miss Bethe Ander- 

 son of Connecticut College, Dr. Esther Carpenter 

 of Smith College, Dr. and Mrs. Warren Lewis of 

 the Carnegie Institution, Dr. Frank Thone of Sci- 

 ence Service, and Harriet Butler Bunker of Dum- 

 merston, Vermont, all of whom examined the early 

 plan, read and criticized the preliminary drafts 

 of the manuscript, made many helpful criticisms 

 and suggestions, and gave me their unstinted en- 

 couragement throughout the task. I should like 

 also to express my gratitude to Professor Gottlieb 

 Haberlandt, Dr. Ross Harrison, Dr. Alexis Carrel, 

 Dr. and Mrs. Warren Lewis, Dr. Walter Kotte, 

 and Dr. Roger Gautheret for permission to use 

 their portraits. These will, I hope, add greatly 

 to the living quality of the book. Dr. Gautheret 

 in particular deserves my deepest gratitude for 

 the difficulties and perhaps danger which he over- 

 came in sending me his picture and biography out 

 of war-ridden Paris. I sincerely regret that Dr. 

 W. J. Robbins preferred to have his portrait 

 omitted from the series. The illustrations, with 



