146 MANUAL OF BACTERIOLOGY. 



typhoid organisms necessary to contaminate a considerable 

 body of water, and sufficient to cause an outbreak of the dis- 

 ease among some of the people drinking the water, may still 

 be so small that many different cubic centimeters of the 

 water might be studied before a single one of the specific organ- 

 isms would be encountered. Anyone who has examined plates 

 made from samples of water will recognize the difficulty of 

 detecting one or a few colonies of the bacteria of cholera or 

 typhoid fever among a hundred or more colonies of ordinary 

 water-bacteria. The existence of contamination with animal 

 excreta might, however, be indicated by finding the bacillus 

 coli communis, whose detection offers a greater prospect of 

 success, the presence of small numbers of the colon bacillus in 

 water is regarded as of little or no significance.* Until our 

 knowledge is more complete, any suspicious water should be 

 discarded. 



Formerly investigators seem to agree that if, using several samples of a water 

 each i c.c. in volume, colon bacilli are found in a majority of the samples the 

 water is probably polluted; if the colon bacillus is only found when larger volumes 

 of water are examined, the results are suspicious though less significant. Some 

 investigators hold that the presence of streptococci in water is indicative of pollu- 

 tion, f At present there seems less agreement upon these points. Johnson $ 

 found that the colon bacillus is ingested by fish when this organism is present 

 in the water in which the fish are kept, and that the bacillus lives and multi- 

 plies in the intestines of the fish. He concludes that in this way fish may 

 convey the colon bacillus, and if so also the typhoid bacillus, from a contami- 

 nated source to an uncontaminated stream. 



Certain devices have been adopted to hasten the develop- 

 ment of the bacteria indicative of pollution and to retard that 

 of the ordinary water-bacteria. Among these may be men- 

 tioned the influence of the heat of the incubator, which will 

 hasten the growth of organisms derived from the human body, 

 and which retards the growth of water-bacteria. Another 



*Jordan. Jaurn. Am. Med. Assn. V. XLVIIL, No. 22. June i, 1907, p. 1861. 

 fPrescott and Baker. Journal o} Infectious Diseases. I. 193. 

 %Journ. Infect. Diseases. Vol. I., pp. 348-354.' 



