DISTRIBUTION OF BACTERIA. 143 



erable body of water, and sufficient to cause an outbreak of 

 the disease 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 organisms would be encountered. Anyone who 

 has examined plates made from samples of water will recog- 

 nize 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 indi- 

 cated by finding the bacillus coli communis, whose detection 

 offers a greater prospect of success. It is not certain just 

 how much importance is to be attributed to the presence of 

 small numbers of the colon bacillus in water. 1 Until our 

 knowledge is more complete any suspicious water should be 

 discarded. 



Certain devices have been adopted to hasten the develop- 

 ment of the desired bacteria and to retard that of the ordi- 

 nary water-bacteria. Among these may be mentioned 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 is 

 the addition of a solution of peptone to a large quantity of 

 the water to be examined with a view to assisting the 

 development of the desired bacteria by furnishing them 

 suitable food for growth. In another method (Parietti's) 

 small quantities of carbolic acid are added to bouillon and 

 mixed with the water, with a view to retarding the develop- 

 ment of all except typhoid and colon bacilli. Suspected bac- 

 teria may be tested by inoculation into animals ; the pos- 

 session of pathogenic properties creates a probability in 

 favor of their having come from some contamination with 

 animal excreta. 



Jordan, Journal of Hygiene, Vol. I., 1901. Savage, Journal of Hy- 

 giene, Vol. II., 1902. Winslow & Hunnewell, Journal Medical Research, 

 Vol. VIII., 1902. 



