234 Bacteriology of Water 



does not throw satisfactory light upon their exact hygienic 

 usefulness. Of course, if cholera or typhoid fever bacteria 

 are present, the water is dangerous, but the quality of the 

 water cannot always be gauged by the number of bacteria it 

 contains. 



Drinking-water, especially that furnished to large cities, 

 is not infrequently contaminated with sewage, and contains 

 intestinal bacteria Bacillus coli communis. For the ready 

 determination of this organism, which is an important indi- 

 cation that the water is polluted, Smith * has made use of 

 the fermentation-tube in addition to the plate. His method 

 is to add to each of several fermentation-tubes containing 

 i per cent, dextrose-bouillon a certain quantity of water. 

 The evolution of 50-60 per cent, of gas by the third day is a 

 strong indication that the colon bacillus is present. Plates 

 may be used to confirm the presence of the bacillus, but are 

 hardly necessary, as there is scarcely another bacterium met 

 with in water that is capable of producing so much gas. 



It was at one time thought that the occurrence of the colon 

 bacillus in water was sufficient to condemn its potability, but 

 the evidence accumulated in recent years, showing that this 

 organism may reach streams from manured soil, may enter 

 it with the dejecta of domestic animals, wild animals, birds, 

 and perhaps even of fishes, makes it doubtful whether any- 

 thing but an exceptionally large number of the organisms 

 should be looked upon as indicative of sewage pollution and 

 proof that the water is not potable. 



In determining the species of bacteria found in the water 

 reference must be made to the numerous monographs upon 

 the subject and to special tables. An excellent table of this 

 kind, arranged by Fuller,! is given on pages 236, 237. 



Filtration with sand, etc., diminishes the number of bac- 

 teria for a time, but, as the organisms multiply in the filter, 

 the benefit is not permanent and the filters must frequently 

 be subjected to bacteriologic tests and the sand washed, 

 spread out to dry and the filters renewed. Porcelain filters 

 seem to be the only positive safeguard, and even these, the 

 best of which seems to be the Pasteur-Chamberland, allow 

 the bacteria to pass through if used too long without proper 

 attention. 



For those whose special line of work is the bacteriology of 

 *"Amer. Jour. Med. Sci.," 1895, 110, p. 301. 

 f " Public Health and Journal of Experimental Medicine." 



