THE STORY OF THE BACTERIA. 



experience that the use of the water may give 

 rise to serious or even fatal acute disorders of 

 the digestive system. Cholera morbus and 

 the so-called winter cholera are apparently 

 sometimes caused in this way. Young chil- 

 dren are especially susceptible to the bad 

 influences of such water, and the boiling of it, 

 or the change of supply, has repeatedly been 

 found sufficient to stop attacks of cholera in- 

 fantum or the summer diarrhoea of young 

 children. 



On the whole, however, the bacteria which 

 water naturally contains as it is found in lakes, 

 running streams, and good springs are quite 

 harmless, unless they are allowed by stagna- 

 tion to accumulate to a very considerable 

 degree. We do not yet definitely know to 

 what extent the ordinary harmless bacteria 

 might be allowed to accumulate in drinking- 

 water before it would become harmful. But 

 the limit is usually somewhat arbitrarily placed 

 at present at from three hundred to five hun- 

 dred to the teaspoonful. 



The frequent real and serious dangers from 

 impure drinking-water do not lie in the bacte- 



