PRODUCTION OF HYDROGEN SULPHIDE 239 



that results of this type would be irregular since many other 

 bacteria aside from colon bacilli are capable of producing hydro- 

 gen sulphide. It would be interesting to determine whether 

 there is any difference in the hydrogen sulphide forming power 

 of pure cultures of colon bacilli coming from different sources. 



Table 3 summarizes the results of a rather complete bacterio- 

 logical analysis of samples of water from various sources, the 

 purpose being to compare the hydrogen sulphide test with 

 standard methods. 



The samples marked "University of Chicago tap" were speci- 

 mens from the Chicago mains. Those marked "University of 

 Chicago filtered" were taken from the University of Chicago 

 drinking fountains, the water having been passed through a 

 special filter belonging to the University. It will be noted that 

 the condition of these waters was very good according to the 

 usual standards, yet a small amount of hydrogen sulphide 

 appeared in one of the filtered samples. 



The samples marked Omaha House 1, 2, 3, 4, 5, and 6, were 

 taken from the taps of houses in a certain district of Omaha, 

 where several cases of typhoid fever had occurred. These 

 analyses were made to determine the condition of the city water 

 supply. Two series of examinations were made about two weeks 

 apart. There was no evidence of contamination according to 

 standard methods yet hydrogen sulphide was formed in two 

 instances in twenty-four hours, and in most other samples there 

 was an appreciable amount of blackening in forty-eight hours. 



These results would indicate that this test is too delicate to be 

 of value in water analysis.. Hydrogen sulphide was formed by 

 every contaminated water and by some waters in which there 

 was no evidence of contamination by the usual methods of 

 examination. This agrees with the results obtained by examina- 

 tion of feces from various animals. 



