Page:Popular Science Monthly Volume 47.djvu/401

Rh same probabilities of degeneration as morbid consanguinity. It appears with nervous, hysterical, and veneric persons, and with criminals, among whom vice becomes the basis of unions leading to progressive degeneracy.

Some infectious diseases, usually propagated by contagion, may be transmitted to the child by the mother, or even by the father, while the mother remains free from them. The disease being due to a special agent of infection, that is, to a being with an existence of its own, such transmission can not, properly speaking, be regarded as a fact of heredity. The generative agents have served only as vehicles for the morbid agent or its products. What has been transmitted is not a natural characteristic, or even a definitely acquired characteristic, but a strange and accidentally imposed property, susceptible of disappearing or of being destroyed. Transmission of this kind does not correspond with the definition of biological heredity. Direct heredity of certain diseases has attracted the attention of observers of all times, and has been most regularly noticed in mental diseases.

The family defect is very often exhibited gradually. One or more generations manifest slight troubles, which we might call preparatory. Heredity has to be accumulated, capitalized, as it were, before displaying itself as a morbid entity to which we can give a name. We often find individuals among the ancestors of insane persons, individuals subject to overexcitement, enthusiasts, originals, unfortunate inventors, dissipated persons, or men of irregular life or afflicted with mental or moral eccentricities.

Heredity is not manifested in the same degree in all the forms of madness, and is less evident in the acute than in the chronic forms. Mental troubles generally are most likely to transmit themselves by heredity when they are active at the moment of conception. They are less surely transmissible if their activity in the progenitors is suspended at the time, and especially if the first attack does not come on till after the birth of the child. The fact that we occasionally see a person who has not yet been insane transmit the predisposition to become so to his descendants demonstrates that it is not the disease itself, but the aptitude to acquire it that is transmitted. Accumulated heredity often results in the production of individuals distinguished by physical malformations or by abnormal emotionalisms, constituting what are called the physical and the psychical stigmata of degeneracy. Yet we can not say that heredity impresses special characteristics on madness. But persons inheriting morbid tendencies are more sensitive to excitement of every kind, and more frequently suffer acute irritations under the influence of insignificant causes, while most usually these irritations disappear as easily and as abruptly as they came on.