DUST AND ITS DANGERS. 37 



of the air in this city, with every twenty 

 breaths one may take into his body, depending 

 upon where he is all the way from u to 376 

 living micro-organisms, together with a variable 

 amount of inorganic dust. 



The number of living germs which the New 

 York citizen is liable to be forced to take into 

 his body, when the streets are dry and the 

 wind blowing, or when the dry filth is being 

 stirred up by careless street-cleaning proced- 

 ures, it would be a difficult and a thankless 

 task to tell. 



Now it has been learned, not only from com- 

 mon experience but from long series of careful 

 experiments, that the solid particles which we 

 breathe in with the air either through the nose 

 or mouth do not come out with the expired air, 

 but are retained on the moist surface upon 

 which the air impinges going in and coming 

 out. These foreign particles floating in the 

 inspired air are caught largely in the nose or 

 mouth or upper throat, while a certain number 

 pass down into the air-tubes and lungs. A 

 large part of this foreign material may be dis- 

 charged from the nose where it is caught in the 



