36 THE POPULAR SCIENCE, MONTHLY. 



the lowest estimate, a tenth of the civilized human race is not 

 very exacting as to the soil afforded. Yet until recently con- 

 sumption 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 hus- 

 bands and wives, roommates, and other persons intimately asso- 

 ciated 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 ad- 

 vantage 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- 



