I9I2.] STOCKARD— CONTROL OF DEVELOPMENT. 195 



abort or produce defective young, while the control animals are 

 giving birth to normal young. Many more cases could be cited if 

 time permitted. 



Experiments on lower animals, therefore, show and human sta- 

 tistics seem to indicate that the cause of structural disease is often 

 an abnormal developmental environment. To prevent such a disease 

 the developmental conditions must be controlled and rendered as 

 nearly normal as possible. 



The second consideration is whether abnormal chemical environ- 

 ment may act on the parental germ cells in such a manner as to 

 cause them to change and become incapable of giving rise to a normal 

 individual. It is well known that certain disease toxins such as that 

 of syphilis and substances such as alcohol and lead effect various 

 body tissues so as to render them unfit for normal physiological 

 activity. It is, therefore, only logical to suppose that the same or 

 similar substances may effect the germ cells and so derange their 

 chemical constitutions as to cause them to give rise to offspring of 

 peculiar structure and qualities. 



Bertholet has found that alcohol has a particular affinity for the 

 reproductive glands just as it does for the nervous system. In 

 examining the structure of the testicles from a large number of 

 chronic alcoholics it was shown that spermatozoa were absent en- 

 tirely or degenerate in form (azoospermy) in a majority of the 

 cases. It is doubtless true that the ability of the spermatozoa to 

 accomplish normal fertilization would be affected long before any 

 definite structural change could be observed. 



The crucial case is the treatment of the male in such a way as 

 to render his spermatozoa unable to produce a normal development 

 when combined with a healthy egg from a normal female. In this 

 case the action must of necessity be on the germ cell only and not 

 on both the egg and emfcryo as it might be in treating a female 

 mammal. 



It must be recognized that an individual owes its structure and 

 character to the peculiar chemical constitution of the germ cells 

 from which it arises. The germ cells of two species of animals are 



