DUST AND ITS DANGERS. 21 



From the enormous number of bacteria and 

 moulds, which are present everywhere in in- 

 habited regions where the conditions are suit- 

 able for their growth, it might be imagined 

 that in dry weather the number of atmospheric 

 germs in the dust out-of-doors would be very 

 great. But this is not usually the case, even 

 in large and populous towns. 



Here and there along the streets, where 

 these are filthy and almost never properly 

 cleaned, or where the wind whirls around the 

 corners of buildings, forming air eddies, the 

 micro-organisms are often present in very large 

 numbers, so that one in passing about the town 

 is apt here and there to encounter veritable 

 germ-showers. But on the whole, almost 

 everywhere out-of-doors, except in dangerously 

 filthy cities, the large volumes of air, which are 

 more or less constantly passing, so largely di- 

 lute the local germ-dusty air that the actual 

 number of micro-organisms in a given volume, 

 say a cubic foot, is on the average very small, 

 and usually insignificant. When the ground 

 is wet and air currents moderate, the number 

 of germs is still further diminished. 



