INTRODUCTION XI 



tendencies of many vegetables so that larger, richer roots 

 grow on Burbank potatoes, more profuse grain on many 

 varieties of wheat and oats, larger and more succulent stalks 

 on sugar cane. He has interfered with the natural reproduc- 

 tion of animals in order to breed cattle with greater quan- 

 tities of muscle for him to eat, pigs with nutritious fat for his 

 table, and hens with a penchant for laying eggs. He has pro- 

 duced abnormalities such as oxen and mules where these 

 better serve some special purpose of his. 



Man also interferes with nature when he kills parasites 

 which might otherwise cause his illness or death, when he 

 eradicates mosquitoes and so avoids malaria and yellow 

 fever, or when he sets one virus to fight another as in vaccina- 

 tion against smallpox. He changes natural processes when 

 he gives anesthetics to deaden pain and when he aids 

 childbirth by mechanical means or by caesarian operation. 

 The whole story of medicine is a history of triumphs over 

 natural forces. Here again, man is beginning to take an 

 interest in even more vital elements of control. He practices 

 birth control; he makes it impossible for certain of the insane 

 and feeble-minded to reproduce their kind. He is beginning 

 to inquire about the possibihty of breeding not only better 

 horses and dogs, but even a finer race of men. Against such 

 proposals many cry: " It is a perversion of nature. " Certainly: 

 but no more so than flying in aeroplanes, using milch cows, 

 growing grapefruit or wiping out the cause of yellow fever. 



What has been done is nothing compared to that which 

 may be just ahead. It is highly important that in such 

 fundamental matters we proceed wisely, cautiously and on 

 the basis of well established facts. Any constructive activity 

 in human biology must rest upon the carefully assembled 

 findings of wise research and must be supported by intelligent 

 pubhc opinion. 



THE CONTENTS OF THIS BOOK 



The papers presented in this volume report the results of 

 investigations in a great group of sciences vitally affecting 

 man. They are intended not only to give a general back- 

 ground and perspective to students of special sciences, 

 but also to give to the average intelHgent layman some 



