The subject is far too wide and complicated to admit of any detailed discussion here. But, explain it as we may, the consoling fact remains that civilized races, including slum-dwellers, have a distinctly lower death-rate from tuberculosis than have savage tribes which are exposed to it even under most favorable climatic and hygienic conditions; that those races which have survived longest in city and even slum surroundings have a lower death-rate than the rest of the community under those conditions; and that certain of our urban populations have lower death-rates than many of our rural ones. As for the immediate effect of heredity in the production of the disease, the general consensus of opinion among thoughtful physicians and sanitarians now is that direct infection is at least five times as frequent a factor as is heredity; that at least eight-tenths of the cases occurring in the children of tuberculous parents are probably due to the direct communication of the disease, and that if the spread of the infection could be prevented, the element of heredity could be practically disregarded. We are inclined to regard even the well-marked tendency of tuberculosis to attack a considerable number of the members of a given family to be due largely, in the first place, to direct infection; secondly, to the fact that that family were all submitted to the same unfavorable environment in the matter of food, of housing, of overwork, or of the New England conscience, with its deadly belief that "Satan finds some mischief still for idle hands to do." Upon direct pathological grounds nothing is more definitely proven than that the actual inheritance of tuberculosis, in the sense of its transmission from a consumptive mother to the unborn child, is one of the rarest of occurrences. On the other hand, the feeling is general that, inasmuch as probably four-fifths of us are repeatedly exposed to the infection of tuberculosis and throw it off without developing a systemic attack of the disease, the development of a generalized infection, such as we term consumption, is in itself a sign of a resisting power below the average. Should such an individual as this become a parent, the strong probability is that his children--unless, as fortunately often happens, their other parent should be as far above the average of vigor and resisting power--would not be likely to inherit more vigor than that possessed by their ancestry. So that upon _a priori_ grounds we should expect to find that the children born of tuberculous parents would be more susceptible to the infection to which they are so sure to be exposed than the average of the race. So that the marriage of consumptives should, unquestionably, upon racial grounds, be discouraged except after they have made a complete recovery and remained well at least five years.