80 FEED W. TANNER 



hydrogen sulfide by bacteria. In a paper by Chamot and Red- 

 field (1915) on the same subject the statement is made that 

 hydrogen sulfide is more rapidly produced in a mixed culture 

 than in a pure culture. The peptone is probably split to abiuret 

 compounds among which are cysteine and cystine. From these 

 it is easy to imagine how H2S may be split off. This reaction 

 has been studied by Sasaki and Otsuka (1912), Burger (1914), 

 and Tanner (1917). 



Action on carbohydrates 



No gas was formed by any of the strains. The reaction in 

 sugar broths was determined after two days' incubation at 37°C. 

 Five cubic centimeters of the media were diluted with 50 cc. 

 of distilled water and titrated, after boihng, with ^ NaOH. 

 Rogers and Davis (1912) commenting on the value of such data 

 for classification work state. 



Mention has already been made of the objections to the use of fer- 

 mentation of sugars and similar substances. The question of the 

 constancy of these reactions has been the subject of investigation, and 

 while there is some disagreement of opinion among those who have 

 studied the question most carefully it seems that they are at least as 

 constant as any of the characters ordinarily used in classification. 



In this study phenolphthalein was used as the indicator, as 

 advised on the 1912 chart of the Society of American Bacteri- 

 ologists. The ideal method would have been the determina- 

 tion of the true acidity by means of the hydrogen electrode, as 

 has been pointed out by the recent work of Clark and his co- 

 workers. 



The rectangular polygons as shown in Diagram II indicate 

 the distribution curves for the various strains with regard to 

 action on glucose, sucrose, lactose and glycerol. 



With regard to glucose, the ciu-ve shows a single mode which 

 indicates one type of fermentative action. None of the strains 

 formed alkali. The distribution curve for the action on sucrose 

 shows a single mode and one single type of bacteria. All of 

 these bacteria are probably non-sucrose fermenters. A single 



