M. H. SOULE 265 



to the removal of the CO,, one obtains the ratio of the gases present. Smith' used the 

 fermentation tube to differentiate three groups of organisms on the basis of the ratios 



TJ CO 



r7\ • (Subsequent workers have usually preferred the ratio-jy^ .) 



I 



Keyes- reviewed the literature of gas analysis and elaborated on the limitation of the 

 Smith tube. The two chief objections to its use are: (i) CO. is very soluble in the 

 medium and a large percentage of that substance actually produced does not appear 

 as a gas. Hence an analysis of the supernatant atmosphere does not give a true indi- 

 cation of the volume of gas produced nor a true ratio between CO. and the other gases. 

 (2) The CO. diffuses from the closed arm through the medium to the open arm and is 

 lost. For these reasons the open fermentation tube has been discarded for use in exact 

 Cjuantitative work. 



Rogers, Clark, and Davis,^ following Keyes, made an exhaustive study of the gas 

 production by members of the colon group. Their cultures were grown in a vacuum, 

 and the dissolved as well as the supernatant gases were estimated. They made no 

 attempt to determine the fixed CO., which, however, must have been appreciable in 



CO, 



amount in spite of the final acidity of the medium. The " ratio in two hundred 



H. 



and sixteen determinations varied from 0.95 to 2.72. In almost all of the analyses 



there was found to be a small but appreciable amount of "residual gas" which they 



called N.. The average amount found for the colon group was about 0.7 per cent of 



the total gas. 



The majority of the quantitative data from studies made on strict anaerobes are 

 open to the criticism emphasized before; the workers analysed only the surface gases. 



Keyes and Gillespie-" employed the exact vacuum method previously described 

 by Keyes, in studying cultures of B. welchii. Bushnell^ presented the gas changes pro- 

 duced by a saprophytic anaerobe. He removed the dissolved gas by evacuation but 

 made no attempt to estimate the fixed CO2. A more thorough investigation of the 

 gaseous metabolism of strict anaerobes was made by Anderson^ who studied twenty- 

 five strains of anaerobic organisms by a modification of the methods of Rogers, Clark, 

 and Davis. 



■ Smith, T.: Cenlralbl.f. BaklcrioL, Abt. I, Orig., 18, 1-9. 1895. 



^ Keyes, F. G. : /. Med. Research, 21, 69-82. 1909. 



3 Rogers, L. A., Clark, W. M., and Davis, B. J.: loc. cit. 



^ Keyes, F. G., and Gillespie, L. J.: J . Biol. Cheni., 13, 291. 1913. 



s Bushnell, L. D.: /. Bad., 7, 373-403. 1922. ^ Anderson, B. G.: loc. cit. 



