PRODUCTION OF HYDROGEN SULPHIDE 249 



dently carbohydrate was a necessary source of carbon for the 

 metabolism of the bacteria. It was omitted in the first medium 

 in order to learn whether the carbon in the ammonium tartrate 

 could serve this purpose. 



Taurin was prepared by the method of Hawk (1918). Its 

 purity was determined by making duplicate analyses for sulphur 

 using the method of Redfield (1912). Theory called for 26.15 

 per cent and we found 25.90 per cent. 



A 0.5 per cent solution of taurin was made in distilled water. 

 It was sterilized with a Berkefeld filter because sterilization by 

 means of heat caused blackening of lead acetate paper, and 

 pointed toward a chemical change in the taurin. Filtration 

 obviated any such possibility. 



Duplicate tubes were inoculated with the same series of organ- 

 isms which were used with the sodium sulphate medium; these 

 were incubated for one week under areobic conditions at 37°C. 

 without growth. 



Another medium was prepared, identical with the above except 

 that 1 per cent of chemically pure glucose was added. After 

 one week's incubation a slight growth appeared in the tubes 

 inoculated with B. proteus-vulgaris, and B. fluorescens-liquifaciens, 

 but not in the others. No blackening of the paper occured in 

 any instance. This would indicate that taurin is not readily 

 attacked by bacteria. 



Cystin was prepared by the method of Matthews and Walker 

 (1909). 



Its purity was ascertained by determining the percentage of 

 sulphur by the same method used for the taurin. Theory called 

 for 26.72 per cent; we found, 27.04 per cent. 



An attempt was made to prepare the ammonium salt of cystin 

 by dissolving the cystin in ammonium hydroxide and evaporating 

 the excess ammonia. The cystin precipitated as soon as the 

 fumes of the ammonia disappeared. Evidently the ammonium 

 salt was easily hydrolyzed. 



The citrate of cystin acted in the same way. In order to keep 

 it in solution an excess of citric acid was required which was 

 sufficient to interfere with bacterial growth. 



