BACTERIA IN WATER 205 



organic and inorganic matters. For water-courses of 

 any character purification is aided by changes in 

 temperature during the day and night and the very 

 efficient disinfecting properties of direct sunlight. 

 Oxygen absorbed from the air also assists in des^roy- 

 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. Domestic 

 filters must be taken care of by some one thoroughly 

 familiar with their operation and cleaning, otherwise 

 they do not deliver safe water. 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 



