TRANSMISSION OF MENTAL QUALITIES. 179 
only in the female line. I scarcely need call to mind how 
exactly the characteristic formation of the face is transmitted 
by inheritance ; sometimes it remains within the male, some- 
times within the female line ; sometimes it is blended in both. 
The phenomena of transmission by inheritance of patho- 
logical conditions, especially of the different forms of human 
diseases, are very instructive and generally known, Diseases 
of the respiratory organs, the glands, and of the nervous 
system, are specially liable to be transmitted by inheritance. 
Very frequently there suddenly appears in an otherwise 
healthy family a disease until then unknown among them ; 
itis produced by external causes, by conditions of life causing 
disease. This disease, brought about in an individual by 
external cause, is propagated and transmitted to his descend- 
ants, and some or all of them then suffer from the same 
disease. In case of diseases of the lungs, for instance in 
consumption, this sad transmission by inheritance is. well 
known, and it is the same with diseases of the liver, with 
syphilis,.and diseases of the mind, The latter are specially 
interesting. Just as peculiar characteristic features of man 
—pride, ambition, frivolity, etc.—are transmitted to the 
descendants strictly by inheritance, so too are the peculiar 
abnormal manifestations of mental activity, which are 
usually called fixed ideas, despondency, imbecility, and 
generally “diseases of the mind.” This distinctly, and 
irrefragably shows that the soul of man, just as the soul 
of animals, is a.purely mechanical activity, the sum of 
the molecular phenomena of motion in the particles of the 
brain, and that it is transmitted by inheritance, together 
with its substratum, just as every other quality of the body 
is materially transmitted by propagation. 
