TKANSMISSIOX OF MENTAL QUALITIES. 1 79 



only in tlie 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 ; 

 it is 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 ]:)ropagation. 



