INHERITANCE OF MENTAL DEFECTS AND DISEASE 49 



alcohol inherit a weak or neurotic physique. The insanity, there- 

 fore, which is credited to the effect of alcohol is doubtless due in 

 many cases to a vitiated inheritance. But it is practically im- 

 possible to measure the relative potency of the hereditary and 

 environmental factors in such cases. And the same statement 

 may be made with respect to the insanity attributed to worry, 

 shock, childbirth, the menopause and the numerous other circum- 

 stances that unbalance the mind. 



There are many forms of insanity differing greatly in their 

 symptoms. Melancholia presents a picture very different from 

 acute mania and dementia praecox. In fact the ills of the mind 

 are almost as varied as the ills of the body. Like the latter they 

 vary continuously in their degree of manifestation from the 

 minor troubles that make people nervous, "a little queer," 

 moody, or excitable, to raging mania or complete dementia. The 

 hereditary forms, while naturally less numerous, present so many 

 degrees of manifestation and so many variations that a satis- 

 factory classification is a matter of great difficulty. 



Some forms of insanity are closely associated with other 

 diseases for which there is a strong heredity proclivity. This is 

 the case with "epileptiform insanity," and to a less degree with 

 "gouty insanity," "phthisical insanity," etc. To speak of heredi- 

 tary insanity as a "unit character" due to a defect or loss of a 

 single character in the germ plasm is about on a par with ascrib- 

 ing all kinds of heritable physical anomalies to the same cause. 

 It may be true that a single defect in the germ plasm may mani- 

 fest itself in a variety of ways and in many degrees. But analogy 

 with the transmission of the bodily traits should make us very 

 cautious about considering the insane diathesis as a unit char- 

 acter of essentially the same kind in the different cases in which it 

 is manifested. Charts of the inheritance of insanity show that 

 the afflicted individuals exhibit a great diversity of symptoms in 

 successive generations. The possibility must, therefore, be borne 

 in mind that the germ plasm of neurotic stocks may be affected 

 in a variety of ways, and that the varied exhibitions of disordered 

 mentality are the result, in part at least, of this circumstance. 



