50 INFECTIOUS AND PARASITIC DISEASES. 



alone in United States, and it is estimated that there 

 are over 2,000,000 of people afflicted with this disease 

 in one form or another. All of these sufferers are 

 expectorating billions of tubercle bacilli daily. Many 

 of them are engaged in earning a livelihood, which takes 

 them into offices and homes, the atmosphere of which 

 they contaminate by coughing, sneezing, and expec- 

 torating. The atmosphere of our cities is vitiated in 

 the same way, but with less danger to others ; for in the 

 open, through the action of sun-light, through heat, 

 dilution, and other physical agencies, the virulence 

 of the bacilli is gradually diminished, and eventually 

 destroyed; finally the bacteria themselves are disinte- 

 grated. But in confined spaces, little or no destruction 

 of the bacilli takes place, so that there ensues in a short 

 time an atmosphere ladened with tubercle bacilli, 

 which is highly dangerous to everyone who breathes 

 it. The dangerous condition of such an atmosphere 

 is attested by the frequency of tuberculosis among 

 successive tenants of a house that was the abode, for a 

 period, of a consumptive. In quiet breathing, no 

 tubercle bacilli are projected into the air, but in sneezing 

 and coughing they are; and in the expectoration, esti- 

 mates of their numbers cannot be placed too high. 

 Thus it is that the tubercle bacilli find their way to 

 the ground, become dry, are ground up with the dust, 

 and with the latter are carried into the air and inhaled. 

 The moral is obvious. 



