CHAPTER XVIII 



HAZARDS OF THE AIR 



THE only way the air which we breathe 

 can be infective, that is, can be the 

 means of transmitting disease-inducing bacte- 

 ria, is, under ordinary conditions, by carrying 

 as dust the dried but living germs from some 

 infected individual or animal along with other 

 and less harmful dust. Thus it is that our 

 recently won knowledge of bacteria and other 

 minute organisms has brought a new sig- 

 nificance into the problems of ventilation. 

 Foul air we still know to be bad and capable 

 of fostering serious susceptibility to disease, 

 but the specific and most significant elements 

 of positive danger are in the floating dust. 



The possibility of taking infective bacteria 

 into the nose, mouth, and lungs with the air 

 out-of-doors, especially in large cities, is 



always with us. But ordinarily the dilution 



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