CHARACTERISTICS OF THE COLOX-AEROGEXES GROUP 79 



tures used consisted of a collection of 689 cultures fermenting 

 dextrose with evolution of gas, without spore formation, 

 with abundant growth on agar and diffused growth in broth. 

 One hundred and fifty-two of these came from 27 samples of 

 human feces, 148 from 17 samples of bovine feces, 132 from 

 31 samples of water, 143 from 33 samples of grains, and 114 

 from milk. They were obtained for the most part by direct 

 plating on asparagin lactose litmus agar followed by replating 

 and a test for fermentation in dextrose or lactose broth. 



THE FORMATION OF GASES 



The active evolution of gases, indicating a more profound 

 fermentation of the carbohydrates, is the striking character 

 which distinguishes the colon-aerogenes group from most of 

 the carbohydrate-fermenting bacteria. The nature and the 

 relative proportion of gases evolved has come to be regarded 

 as of little significance and the fermentation tube of Theobald 

 Smith is now used merely to determine the fact of gas pro- 

 duction. The gas ratio, proposed by Smith 2 as a diagnostic 

 character, has fallen into disrepute through its failure to 

 correlate with habitat or with other physiological characters. 

 This attitude is well illustrated by the paper by Longlej* and 

 Baton. a The probable cause of this failure is found in the 

 work of Keyes 4 who pointed out the great variation in the 

 gas ratio as ordinarily determined and its constancy when 

 determined by accurate methods. Our results have confirmed 

 the conclusions of Keyes in every way and show that the 

 nature and amount of the gaseous by-products formed under 

 uniform conditions are remarkably constant. 



The same culture, or even different cultures of the same 

 variety, will repeat the ratio of carbon dioxide to hydrogen 

 with almost mathematical accuracy. This is illustrated by 



* Theobald Smith, The Fermentation Tube with Special Reference to 

 Anaerobiosis and Gas Production among Bacteria in Wilder Quarter-Cen- 

 tury Book, pp. 187-232, 1893. 



3 F. F. Longley and W. U. C. Baton, Notes on the Determination of B. 

 Coli in Wafer in Jour. Inf. Dis., 4, 3, pp. 397-416, 1907. 



4 Frederick G. Keyes, The Gas Production of Bacillus Coli in Jour. Med. 

 Res., 21, 1, pp. 69-82, 1909. 



