THE BACTERIA OF SOIL, AIR, WATER, ETC. 139 



Bacteria of Water and of Ice. The water of rivers, lakes 

 and the ocean always contains bacteria. The number of 

 organisms varies greatly in different places and under dif- 

 ferent conditions. The number of different species found in 

 water is also very large. Ground-water* contains few or no 

 bacteria under normal conditions, and is therefore suitable for 

 a source of water-supply, when a sufficient amount is available. 

 The possibility of contamination of the ground-water from 

 unusual or abnormal conditions should always be eliminated 

 before it is taken for drinking-water. Numerous epidemics of 

 typhoid fever have been traced to contamination of wells. 

 The location of wells with reference to privy-vaults, and other 

 possible sources of contamination should be chosen with the 

 greatest care. 



The ordinary bacteria of waterf are harmless, -as far as is 

 known. Bad ordors and tastes in drinking water that is not 

 polluted with putrid material are usually due to minute green 

 plants (algae). J The diseases most commonly disseminated 

 by water are typhoid fever and Asiatic cholera, and probably 

 also dysentery. The results of experiments testing the 

 length of time which the cholera spirillum and the typhoid 

 bacillus may persist in water are conflicting. Many epidemics 

 of cholera and typhoid have been traced to water polluted with 

 the discharges from cases of these diseases. 



By self -purification of water is meant the removal through 

 natural processes of contaminating organisms such as might 

 occur from the discharge of sewage into it. It depends upon 

 the sedimentation of the contaminating material, in the form 



*Ground-water is the water which originally derived from rain or snow 

 sinks through superficial porous strata, like gravel, and collects on some under- 

 lying, impervious bed of clay or rock. 



fSee Fuller and Johnson The Classification of Water Bacteria. Journal 

 o} Experimental Medicine. Vol. IV., p. 609. Jordan. Journal of Hygiene. 

 Vol. III., Jan., 1903. 



|G. T. Moore. Contamination of Water Supplies by Alga?. Yearbook 

 U. S. Department of Agriculture. 1902. 



