Page:Popular Science Monthly Volume 47.djvu/405

Rh but many persons who exhibit the characteristics of this category have not inherited them. The necessity of this connection between degeneration and heredity ought to disappear along with the notion of inevitable heredity. We may degenerate without a hereditary tendency thereto, and we may escape morbid heredity. Diseases which are developed simply on account of a hereditary or congenital disposition constitute manifestations of a tendency to degeneration. Morel showed long ago that a race of insane, whatever its origin, tends to exhaust itself in the fourth generation. The fact is found to apply to other hereditary diseases. The tendency to become sterile is, like dissimilarity, an indication of the diminishing vitality which constitutes degeneration, and may be found in plant as well as in animal species. Mr. Dixon has shown, as Morel demonstrated for pathological families, that mulatto stocks die out unless they are crossed with negroes or with whites, and the fourth generation usually marks the limit of their continuance. We have, therefore, a right to infer that it is by degeneration that various diseases which rarely arise except in consequence of a morbid predisposition are met with in the same families.

Congenital malformations act also frequently like the diseases with which they are found associated. Teratological heredity includes facts very like those which have been marked in pathological heredity. While we observe such malformations as sexdigitism, syndactyly, and ectrodactyly transmitted directly for several generations, we more usually see different deformities in the same family. This is because the malformation may vary in form and seat according to the age of the embryo in which a disorder of nutrition is produced. It has even been assumed that variation of species may have had a teratological origin; but we are acquainted with very few deformities that have been definitely established. If the tailless cats of Japan and the Isle of Man are of teratological origin, they constitute a unique exception. While we often observe various deformities in the same family, it is not more rare to meet a number of anomalies in the same person—a phenomenon which deserves special attention.

Most of the deformities compatible with life may be coincident with affections of the nervous system; and the patients whose nervous systems are most gravely affected are just those who present multiple deformities; idiots and imbeciles nearly always exhibit congenital anomalies, which likewise frequently occur in deafmutes, epileptics, etc. The anomalies found in the insane are less gross, but appear more frequently in proportion as the morphology of that class of patients is more carefully studied. The study of physical anomalies in neuropaths, though they are not less common, is still more frequently neglected. With epileptics who