DISEASE GERMS 



criminal carelessness, because in the eye of the law 

 ignorance is not accepted as an excuse. Somewhere 

 there has been neglect of the cleanness or care which 

 ought to have made infection impossible. 



When rain starts from the clouds it is pure, but in 

 falling through the air it washes out from the air large 

 quantities of dust, so that the first fall of any shower 

 is very dirty. Where rain water is collected for drink- 

 ing or cooking purposes this first fall should be allowed 

 to waste or the whole be thoroughly filtered before 

 its use in cooking. The cistern also must be kept clean 

 and free from dust pollution. It should be sheltered, 

 but not air-tight. Such a water supply is seldom pol- 

 luted by sewage or any human wastes. It is water 

 running on the surface of the ground or draining 

 through it which may encounter sewage pollution and 

 thus be most liable to take up disease germs. 



Snow filters the air even more than rain, each con- 

 gealed flake usually containing many bacteria. The 

 first snow, although white and pure to look at, is not 

 clean and should not be used as a source of drinking 

 water except in emergencies. However, after the snow 

 has been falling for some time the water from it is 

 practically clean. 



Light always retards and in many cases prevents 

 the development of harmful micro-organisms. But this 

 disinfectant action does not extend to all depths, prob- 

 ably not much beyond nine feet, so that its purifying 

 agency in open water supplies is only partial. A water 



Pollution 

 of Water 



Effect 

 of Light 



