PREFACE 



The essays contained in this volume were written on differ- 

 ent occasions mostly in response to requests for a popular 

 presentation of the results of the author's investigations. The 

 title of the volume characterizes their general tendency as an 

 attempt to analyze life from a purely physico-chemical view- 

 point. Since they deal to a large extent with the personal 

 work of the author, repetition was unavoidable, but in view of 

 the technical difficulties presented by some of the topics this 

 may serve to facilitate the understanding of the subject. 



The author wishes to thank the editors and publishers who 

 gave their consent to the reprinting of these essays: Professor 

 J. McKeen Cattell, of Columbia University, Professor Albert 

 Charles Seward, of the University of Cambridge, England, 

 Ginn & Co., of Boston, G. P. Putnam's Sons, of New York and 

 London, and the J. B. Lippincott Company, Philadelphia. 



The Rockefeller Institute 



FOR Medical Research 



April 4, 1912 



