EURAL ENGINEERING. 285 



time. The method tested consisted of adding a peptone and salt solution to 

 the water and observing the effect on a strip of paper impregnated with lead 

 carbonate and suspended over the mixture after incubating at 37° C. for 24 

 hours. 



It was found that irrespective of the inorganic salts present and of the 

 acidity of the medium a concentration of between 3 and 4 per cent of peptone 

 in the final inoculated and incubated medium appeared to favor the most rapid 

 and energetic production of hydrogen sulphid. The addition of beef broth to 

 simple peptone media slightly increased its sensitiveness, but not in proportion 

 to the increased trouble and labor involved. " If sodium chlorid is used, the 

 quantity added must not be over 3.5 per cent." Cultures to which this salt 

 was added showed greater hydrogen sulphid production than those which con- 

 tained none. In 3 per cent peptone media, the presence of from 0.5 to 1 per 

 per cent of potassium chlorid had a decidedly beneficial influence and led to 

 quicker, better, and far more uniform results than any other inorganic salt 

 tried. 



" Positive results of hydrogen sulphid formation may be obtained In 18 

 hours. No hydrogen sulphid formation is obtainable in as long a period as 

 72 hours from natural waters which are truly ' clean,' while much is formed 

 in from 12 to 24 hours with contaminated waters. The feces of domestic 

 animals contain bacteria which are capable of producing hydrogen sulphid 

 from a simple peptone medium in as large amounts as is the case of the 

 bacteria from human feces. The large amounts of hydrogen sulphid rapidly 

 produced by organisms of sewage appears to be not due primarily to members 

 of the Bacillus coli group. This group of hydrogen sulphid-producing bacteria 

 does not actively ferment carbohydrates. Hence testing for their presence is 

 a valuable aid supplementing tests for gas producers and is of especial value 

 in polluted waters in which the B. coli group is absent. Some evidence has 

 been obtained which apparently indicates that hydrogen sulphid is more rapidly 

 produced in waters containing a mixed bacterial flora than by the isolated pure 

 cultures alone." 



Studies on the culture media employed for the bacteriological examination 

 of water, II, E. M. Chamot and C. M. Shebwood {Jour. Amer. Chem. Sac, 

 37 {1915), No. 8, pp. 19^9-1959, figs. 4)- — In continuation of the experiments 

 noted above tests were made of the lactose-peptone media. 



The results showed that " in the fermentation of lactose by bacteria in water 

 contaminated by sewage, human feces, the feces of domestic animals, and pure 

 strains of the Bacillus coli group, the total volume of gas formed increases to 

 a final maximum with the concentration of the peptone, meat, liver, or meat 

 extract employed. The composition of the gas formed is dependent upon the 

 concentration of the nitrogen-containing substance employed. 



" The addition of from 0.5 to 1 per cent of potassium chlorid to lactose-peptone 

 media appears to stimulate fermentation and assure more uniform results. 

 Similar beneficial efiiects are obtainable with sodium chlorid, but of not so 

 marked a character. Nothing is to be gained by employing a lactose concen- 

 tration of over 1 per cent. Neutral media appear to yield slightly greater 

 gas volumes than media slightly acid to phenolphthalein, but media having a 

 reaction of approximately + 1 per cent ferment considerably more rapidly and 

 yield diagnostic results in several hours' shorter time. 



"The gas ratios of organisms of the B. coli group are dependent upon the 



concentration of the peptone or other similar nitrogenous material in the 



media. The addition of meat infusion to peptone media improves this media 



when low concentrations of peptone are employed, but yields media whose re- 



22434°— No. 3—16 7 



