sitic or suspected to be so, like tuberculosis and cancer, appear more frequently in the same families. The last coincidence may be explained by the fact that the system of nerves regulating nutrition may, when its activity is weak, diminish the resistance of the organism and favor the action of morbid agents.
The question of morbid heredity is still more complicated by the established facts that in a large number of tainted families there exist individuals wholly exempt, while the exceptional character of their cases can not be interpreted by the uncertainties of paternity; and that a considerable number of affections usually regarded as hereditary or peculiar to the family may appear in a family independently of all heredity. Many diseases are known that merit the title of family disorders and attack several children of a single generation without its being possible to find anything like them in either the paternal or the maternal line. The persistence of healthy individuals in an unhealthy family may be explained by atavism; but the appearance of a family disease without any resemblance among the ascendants constitutes an exception to the laws of normal heredity.
We are justified in charging certain toxic or infectious agents with being capable of determining, by the influence they exercise upon progenitors, the same morbid predispositions as heredity. Thus, we can attribute to chronic alcoholism, to saturnism, to morphinism, and to other habits of intoxication of parents a considerable number of nervous affections and psychopathies which are developed in the children at different ages, and confer upon them characters quite different from the characters of their parents. Acute transitory intoxications may have the same effect; and drunkenness of parents at the moment of conception or during gestation has been charged with producing imbecility, idiocy, epilepsy, and other diseases in the children.
The effect of intoxication by drugs may likewise be induced by emotional intoxication. The acute or chronic emotions of the mother during gestation may undoubtedly have a noxious influence upon the child and determine troubles of development in it, which may be manifested by anomalies of forms or by functional troubles revealing anomalies of structure. Bad food or defective hygiene, acting directly upon the nutrition of the mother, may have the same effects. All these conditions, finally, may be accumulated under certain circumstances.
In short, the predisposition to disease may be hereditary or congenital. Hereditary transmission is, however, not inevitable, and most frequently it is due to very diverse conditions in the nutrition of the progenitors. Some authors have associated the idea of degeneration with that of heredity, and designate a whole category of disorders under the name of hereditary degenerations;
