The phenomena of transmission by inheritance of pathological 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 descendants, 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.