The _body-cells_ are greatly changed by disease, poison, injury, and overwork, but these changes are not passed on, and despite the influence of disease from time immemorial, the _germ-cell_ produces the same man as in ancient days. Without this fixity of character, this "continuity of the germ-plasm", "man" would cease to be, for the descendants of changeable cells would be of infinite variety, having fixity of neither form nor character.
Epilepsy, hysteria and neurasthenia are all outward signs of defect in the germ-plasm, and so they (or a predisposition to them) can be passed on, and inherited.
If a man shows a certain character, his plasm, had, and has, the causative factor. He may have received it from _both_ his parents, when it will be _strong_, or from one only, when it will be _normal_. If he have it not, it is absent. The same applies to the plasm of the woman he mates, so there are six possible combinations, with results according to "Mendel's Law."
_All_ the children will not inherit a taint unless _both_ parents possess it, but, however strong one parent be, if the other is tainted, _none_ of the children can be absolutely clean, but will show the taint, weak, strong, or dormant. This means that neuropathy will recur--and that it has previously occurred--in the same family, unless there be continual mating into sound stocks. If there is continual mating into bad stocks, it will recur frequently and in severe forms. All intermediate stages may occur, depending entirely on the qualities of the combining stocks.
From this we shall expect, in the same stock, signs of neuropathic taint other than the three diseases dealt with here, and these we get; for alcoholism, criminality, chorea, deformities, insanity and other brain diseases, are not infrequent among the relatives of a neuropath, showing that the family germ-plasm is unsound.
Epilepsy, one symptom of taint, is more or less interchangeable with other defects; the taint, as a whole, is an inheritable unit whose inheritance will appear as any one of many defects. This is shown by the fact that very few epileptics have an epileptic parent. Starr's analysis of 700 cases of epilepsy emphasizes this point.
Epilepsy in a parent 6 Epilepsy in a near relative 136 Alcoholism in a parent 120 Nervous Diseases in family 118 Rheumatism and Tuberculosis 184 Combinations of above diseases 142