Bearing this in mind, let us consider briefly some of the causes above mentioned. I. HEREDITY.--That the child inherits from its parents its physical {176} type, including color, stature, physiognomy, temperament, and certain peculiarities of structure or arrangement of internal organs, is well known. This hereditary influence is stronger from the immediate than from the remote ancestry, although the curious phenomena of atavism sometimes form exceptions to this rule. The hereditary causes of disease can be guarded against when known. Theoretically, by preventing generation on the part of persons who are unfit to produce offspring; practically, to a certain extent, by taking special precautions against these causes and their effects in the individual, particularly at those ages in which these influences seem to have their greatest force. The most important of these hereditary diseases are syphilis, consumption, scrofula, cancer, gout, certain skin diseases, insanity, and criminal tendencies of various kinds. The physician's advice is rarely asked with regard to the propriety, from a sanitary point of view, of a proposed marriage, nor is it often taken when given, unless, indeed, it happens to correspond with the wishes of the recipient; nevertheless, he is occasionally in a position to exert influence in such a matter, and when this is the case the following general rules may be borne in mind: 1. No marriage should occur between persons having the same hereditary tendency to disease; and this is especially important in marriages between relatives. 2. A girl should not marry under the age of twenty. 3. A person affected with hereditary or well-marked constitutional syphilis, or having a strong consumptive taint, or tendency to mental unsoundness, should not marry at all. The precautions to be taken in individual cases in which there is a known hereditary predisposition to certain diseases will probably be indicated in the articles upon those special diseases. The most important of these, from the sanitary point of view, are consumption and gout, partly because of their frequency, partly because of the undoubted power which a proper regimen, applied in time, has in controlling them. The pain in gout has often an excellent sanitary effect; it is an inducement to temperance much stronger than any amount of good advice. The influence of heredity in producing abnormities of refraction and accommodation of the eye, and the importance of detecting these early and giving them proper treatment, have not hitherto received, from the general practitioner, the attention which they deserve. Children of parents affected with astigmatism, ametropia, etc. should be carefully examined before being placed at school, and if necessary fitted with proper glasses.