126 MANUAL OF BACTERIOLOGY. 



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 loca- 

 tion of wells with reference to privy- vaults and other possible 

 sources of contamination should be chosen with the greatest 

 care. 



The ordinary bacteria of water* are harmless, as far as is 

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

 polluted with putrid material are usually due to minute green 

 plants (algae). t 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 dis- 

 charges 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 of 

 mud, upon the growth of the ordinary water-plants and pro- 

 tozoa, upon the exhaustion of the food supply by the growth 

 of bacteria themselves, upon the destructive influence of direct 

 sunlight, and the dilution of the matter added with a large 

 volume of water. J It is not usually to be relied upon as a means 

 of freeing the water-supply from pathogenic bacteria. 



* See Fuller and Johnson. The Classification of Water Bacteria. Journal 

 of Experimental Medicine. Vol. IV. p. 609. Jordan. Journal of Hygiene. Vol. 

 III. Jan., 1903. 



t G. T. Moore. Contamination of Water Supplies by Algse. Yearbook 

 U. S. Department of Agriculture. 1902. 



i See Jordan. Journal of Experimental Medicine. Vol. V., p. 271. 



