the lowest estimate, a tenth—of the civilized human race is not very exacting as to the soil afforded. Yet until recently consumption has not been recognized as a contagious disease, and the factor of predisposition, as determined by heredity, lack of proper air and exercise, failure of vital strength, impoverished blood, "weak lungs," etc., has been considered paramount. It is certainly true that a robust person may be placed in the most intimate contact with the germs of tuberculosis and throw them off or inclose them as inert foreign bodies in his tissues; on the other hand, nearly every one is at one time or another susceptible to tuberculosis and escapes or becomes a victim according as he is free from or is exposed to contagious influences. A mother and her baby, for instance, both die of consumption and heredity is blamed. But does the child inherit the bacilli, or does it imbibe them in the milk—where they have been repeatedly found—or are they inhaled as the mother bends over the child and smothers it with kisses? Again, brothers and sisters drop off' one after another, and it is said that "consumption runs in the family"; but we would seek another explanation if the same succession of deaths were due to scarlet fever. Tubercle bacilli have been found in the dust on the top of the door and window casings, in carpets, bedding, and wall paper. Is it not rational to suppose that these foci of infection have more to do with the death of successive members of the family than a hereditary taint? When we note that members of the family who leave home escape the disease and that other persons occupying the same house later contract it, is not the evidence tolerably clear? Are not husbands and wives, roommates, and other persons intimately associated almost as likely to follow one another with consumption as if there were a blood relationship? Such questions can only be fully answered by a careful collection of statistics, taking advantage of the experiments of chance; enough evidence has been already gathered to warrant the adoption of the contagiousness of tuberculosis as a practical basis for preventive measures.
The predisposing tendencies to tuberculosis may be modified, often absolutely removed, by hygienic and tonic treatment. If, however, any systematic attempt is to be made to stamp out the disease, such an attempt as has been eminently successful in the case of cholera and smallpox, it must depend upon isolation and disinfection. We may logically hope to be able to vaccinate against any disease which occurs but once in a lifetime—that is to say, we may dwarf the germs so that their growth will occasion no dangerous symptoms while they will still "exhaust the soil" so as to prevent a subsequent development of the corresponding unmitigated germs. This hope has been realized only in the case of smallpox, but it is quite likely that the bacteriological horti-
