PRODUCTION OF HYDROGEN SULPHIDE 233 



stir constantly until as much of the peptone as will do so has gone 

 into solution. Cool rapidly and make up to 1 liter with tap water. 

 Transfer to a flask, heat to boiling again, plug, cool rapidly, and place 

 in the ice box for at least twenty-four hours. Filter cold through paper 

 and distribute in 10 cc. amounts among the special flasks suggested. 

 Sterilize the flasks in the autoclave at one atmosphere for fifteen minutes. 

 When cool, place in the tube of each flask a strip of bibulous paper 25 mm. 

 in length, which had previously been impregnated with lead acetate. 



The top of the plugged tube was then closed by wrapping with 

 a strip of tin foil. The flasks alluded to were of a special design. 

 They were shaped like a Sohxlet extraction flask, were graduated 

 at 90 cc. and 100 cc. and a ground glass cap ending in a narrow 

 tube was fitted over the neck of each flask. 



Redfield tested this method by means of an artificial sewage, 

 prepared from human feces. This sewage was quite dilute, since 

 it contained only twenty colon bacilli per cubic centimeter and 

 had a total bacterial count of twenty-eight hundred. He re- 

 ports a gradual increase in the amount of hydrogen sulphide pro- 

 duced, and in the speed of its production as the concentration of 

 sewage increases. The same result is reported with a consider- 

 able number of untreated waters from a variety of sources. He 

 concludes that there is a uniform relationship between the de- 

 gree of pollution of a water and the amount of lead acetate paper 

 blackened when this method is employed. 



Redfield also made some quantitative determinations of the 

 amount of hydrogen sulphide produced by sewage organisms. 

 He compared a number of methods for the quantitative determi- 

 nation of sulphur in peptone solutions. He also investigated the 

 hydrogen sulphide producing powers of several species of bacteria, 

 and concluded that the proteolytic organisms rather than B. coli 

 are responsible for its formation. 



Burnet and Weissenbach (1915) suggest another use for the 

 hydrogen sulphide producing powers of bacteria. They found 

 that colonies of B. paratyphosus B, became black when grown on 

 agar which contained a small amount of lead acetate, while 

 colonies of B. paratyphosus A did not. They consider this an 

 accurate method for the differentiation of the two organisms. 



