192 BACTERIA IN AIR, SOIL, WATER, AND MILK 



efficient disinfecting properties of direct sunlight. 

 Oxygen absorbed from the air also assists in destroy- 

 ing bacteria. There are certain saprophytes in water 

 and sewage capable of breaking up organic matter and 

 freeing oxygen, which, either free or in going into com- 

 bination with other elements in chemical union, is 

 inimical to pathogenic non-spore-forming bacteria. 



In this book a word may be useful as to the means 

 of artificially purifying water for domestic purposes. 

 For the community water is purified by settling in 

 reservoirs, or by filtration through sand and stones, 

 sometimes aided by the addition of chemicals. For 

 household purposes bacteria in water may be removed 

 by house filters made of porcelain attached to the 

 house supply, or what is better, by boiling. The flat 

 taste of boiled water may be removed by allowing air 

 to go through by pouring from one container to another 

 several times. 



Water in a shallow vessel, preferably of copper, will 

 be practically sterilized by an hour's exposure to direct 

 sunlight. This is practicable for camping parties who 

 are compelled to use water under suspicion. 



Principal Water-borne Diseases. The principal dis- 

 eases transmitted by water are typhoid, cholera, and 

 dysentery. Typhoid bacilli may live in water, espe- 

 cially if surrounded by a bit of protective and nutrient 

 organic matter, for many weeks. The question is 

 often asked as to how a few germs in a glass or two 

 of water can cause typhoid fever. As a matter of 

 fact, when an epidemic of typhoid is starting there are 

 usually supposed to be many germs and not a few 

 in the water. What probably happens is that a small 



