PRODUCTION OF HYDROGEN SULPHIDE 251 



Probably nearly neutral solutions of cystin in citric acid, in 

 tartaric acid, or in ammonium hydroxide, prepared as in the 

 case of the sodium carbonate solution, would have given similar 

 results but these methods were not tried. The work done seemed 

 to indicate that organic sulphur in the partially reduced con- 

 dition rather than in the oxidized forms gives rise to hydrogen 

 sulphide when ordinary bacteria act on protein. 



SUMMARY 



The examination of a number of samples of feces showed no 

 constant difference between the amount of hydrogen sulphide 

 produced by human and animal fecal material. This indicates 

 that a test of samples of water for hydrogen sulphide production 

 would be of no value in distinguishing between human and 

 animal contamination. 



The hydrogen sulphide test is too delicate for use in examina- 

 tion of water for the detection of fecal contamination of any 

 type. All contaminated waters examined were positive to this 

 test and many were positive which gave no evidence of con- 

 tamination by the usual criteria. 



A considerable number of common bacteria were able to pro- 

 duce hydrogen sulphide from Witte peptone and not from Difco 

 peptone and some other kinds were able to produce it in larger 

 amounts. Fairchild's peptone yielded more hydrogen sulphide 

 than did Difco peptone. This emphasizes the need for uniform 

 media. 



Glucose and lactose had little effect on hydrogen sulphide 

 formation. There was little difference between 3 per cent, 

 peptone solutions and standard beef extract broth. 



All strains of B. paratyphosus B examined, produced hydrogen 

 sulphide in twenty-four hours or less, while none of the strains 

 of B. paratyphosus A were able to do this. 



All strains of B. typhosus studied produced hydrogen sulphide 

 in twenty-four hours or less and none of the strains of B. dyseiv- 

 teriae had this power. 



Sodium sulphate was not a source of hydrogen sulphide in the 

 limited number of experiments made. 



