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 precox. 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. 
