282 BACTERIOLOGICAL EXAMINATIONS 



The fewer the number of other bacteria the longer will typhoid 

 live. They can live many days in ordinary river water. 



Ice may contain great numbers of bacteria; it is well known 

 that freezing does not destroy pathogenic bacteria, such as the 

 typhoid bacillus. Prudden found typhoid bacilli in ice after one 

 hundred days, although the number was greatly reduced over that 

 placed in the ice originally. Many are squeezed out by contraction 

 of the water. The greatest danger from ice is in dirty handling. 



Disposal of sewage is a bacteriological process in many cases; 

 either the sewage may be treated in sand niters or it may be run 

 put on land where over 200,000 gallons may be disposed of on an 

 acre of land a day. As far as possible nature should be imitated 

 in every way and the breaking up of masses of matter in sewage 

 may be accomplished in the septic-tank process in which active 

 oxidization of the matter is accomplished by bacteria. It appears 

 from the observations of many sanitarians that both aerobic and 

 anaerobic bacteria are necessary to finally reduce sewage to the 

 elementary gases and pure water. 



In the interior of closed tanks and in the depths of sand niters 

 anaerobic conditions prevail. On beds of coke, and on the sur- 

 face of sand filters, aerobic conditions obtain. The effluent from 

 a septic-tank sewage-disposal plant is very often pure water from 

 both chemical and bacteriological standpoints, due to the chem- 

 ical action of the bacteria. 



Bacteriology of the Air 



That the lower layers of the earth's atmosphere contain many 

 bacteria is well known. The air over the sea and over mountain 

 ranges is freer from bacteria than the air over arable lands and 

 large cities. 



When air is still and confined, all bacteria, according to Tyndall, 

 gravitate to the ground, and the air above becomes quite sterile. 

 The atmosphere of sick rooms, hospitals, public conveyances, 

 theatres, etc., contains many bacteria and often pathogenic ones. 



