HEREDITY AND MANIC-DEPRESSIVE PSYCHOSES 



337 



constitutional tendency towards mental disease. If, on the other hand, the 

 proportion of affected individuals in such group was equal or sensibly less, 

 it would be necessary to look elsewhere than in heredity for an explanation 

 of the origin of the disease. 



In an earlier study we defined the expectation of mental disease as the 

 chance of an individual being treated in a hospital for mental disorders in 

 the course of a life time. In accordance with this definition it was found 

 that in 1920 in the State of New York, males had 4.7 chances in a hundred 



TABLE 3 



Frequency of mental and nervous diseases and dejects among relatives of 60 male 

 manic-depressives 



One individual may have more than one defect or disease. 



of becoming insane, females 4.4 chances in a hundred. On the theory of 

 random sampling, therefore, approximately 4.7 per cent of our male popu- 

 lations, and 4.4 per cent of our female populations should develop psychoses 

 necessitating the admission of these individuals to a hospital for mental 

 diseases. Since the expectation of mental disease has been increasing from 

 decade to decade, these rates are probably too high for the older generations. 

 However, this is counterbalanced in our family statistics by the fact that 

 some individuals who were undoubtedly psychotic were not treated in insti- 



