FOREWORD 



Dr. Raymond Pearl, Professor of Biology, School of Hygiene 

 and Public Health, Johns Hopkins University, delivered the- 

 Patten Foundation Lectures at Indiana University in October, 

 1938. It was his intention to expand these five lectures before 

 final publication. Other duties interfered and the work was left 

 incomplete at the time of his death, November 17, 1940. 

 Mrs. Pearl, with the help of some of Dr. Pearl's friends, re- 

 edited the manuscript and gave it to the University in its 

 present form. In presenting the manuscript, Mrs. Pearl recog- 

 nized its incompleteness and even its imperfections, for no one 

 could do the task as Dr. Pearl, himself, would have done it. 



F. Payne 



