CHAPTER III 



THE INHERITANCE OF MENTAL DEFECTS AND 



DISEASE 



"Our human civilized stock is far more weakly through congenital 

 imperfection than that of any other species of animals, whether wild or 

 domestic." — Francis Galton, Inquiries into Human Faculty. 



That many forms of mental deficiency and disorder are capable 

 of hereditary transmission, has long been recognized, but it is 

 only recently that attempts have been made to discover the 

 precise rules according to which such transmission takes place. 

 Much, however, still remains obscure in regard to this important 

 topic. The vast literature on the subject contained in works on 

 medicine and pathology, in numerous medical journals and va- 

 rious other publications consists mainly in the discussion of iso- 

 lated cases of transmission, or the compilation of mass statistics 

 from the records of institutions for the care of the mentally ab- 

 normal. Institutional records being often gathered in a more or 

 less perfunctory manner, and by many different persons, are apt 

 to include numerous inaccuracies and are pretty sure to fall short 

 of the desired degree of fullness. The relatives of mental defec- 

 tives from motives of family pride frequently conceal the exist- 

 ence of defects in other members of the family, and even when 

 they honestly attempt to give all the information they possess 

 they often fail to furnish data of any value. 



It is not surprising, therefore, to encounter wide differences of 

 opinion among authorities concerning the extent to which various 

 forms of defect depend upon a hereditary diathesis. Practically 

 everyone whose opinion is of any value concedes to heredity a 

 certain role in the causation of neuropathic traits. A part of the 

 difference of opinion doubtless depends upon the circumstance 

 that the relative potency of hereditary and environmental factors 



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