248 BACTERIA, YEASTS, AND MOLDS 



for their drinking supplies. The result of drinking such 

 contaminated water is the development of many cases of 

 typhoid fever. A large part of the cases of this disease in 

 cities are due to the contamination of drinking water. Many 

 epidemics have been traced to just such a source. 



The Asiatic cholera bacillus (Fig. 75) has also in recent 

 years been shown to be distributed by means of the water 

 supply. The practical result of this discovery has been 

 that, since cities have learned to guard their water sup- 

 plies, severe epidemics of cholera have been prevented. 

 ^ This subject, however, need not detain us, 



^'^^0 ^C?^ ^s the disease is hardly known in America. 

 ^^^>^ But in the event of a cholera epidemic 

 it should be remembered that the majority 

 .75. ac us ^£ cases are due to drinking water that 



of cholera. ° 



has been contaminated with cholera bacilli. 



There are some other diseases occasionally distributed 

 by water, but they are rare or little known. We need not 

 consider them in our discussion. 



The practical question how to avoid such dangers must 

 face the head of every household. To answer this we 

 must first fully realize that any water which has oppor- 

 tunity for sewage contamination is dangerous for drink- 

 ing, and cities supplied only with water directly from 

 rivers or streams have a supply that is frequently unsafe 

 for use. Those cities, however, which have large reser- 

 voirs where the water stands for some time will have 

 more reliable water, since the standing of water will in 

 time always purify it of typhoid bacilli. The danger that 

 the water supply may become a source of typhoid fever is, 

 therefore, confined to those cities that use the water of 



