CHARACTERISTICS OF THE COLON-AEROGENES GROUP 83 



in the gas produced by the low ratio group, a similar change 

 in the composition of the medium materially affected the gas 

 ratio of the high ratio group by increasing the C(X. The 

 possibility of distinct fermentations, one producing CO 2 

 and H 2 in equal parts and one producing CO 2 independently 

 of the hydrogen, is strengthened by the fermentation observed 

 in the third group which gives carbon dioxide only and for 

 which the ratio may, for convenience, be designated by the 

 a sign. Only twelve cultures of this type were found, but 

 the unusual end product of their fermentation entitles them 

 to consideration as a separate type. 



The statement by Burton and Rettger 6 that we believe that 

 the two reactions are mutually dependent does not express the 

 opinion we have held on this subject. On the contrary we 

 have found considerable evidence to lead us to believe that 

 these fermentations were independent. Burton and Rettger 

 have taken a similar view and have elaborated an hypothesis 

 to account for the two fermentations. They assume that in 

 one fermentation nearly equal volumes of carbon dioxide 

 and hydrogen are produced with sufficient acidity to suppress 

 the second fermentation when the former predominates. In 

 the second fermentation butylene glycol is fermented with 

 the formation of considerable quantities of gas and acetyl- 

 methyl-carbinol, the substance giving the Voges-Proskauer 

 reaction. Since the end products of the reaction are not acid 

 in their character, a proteolysis is permitted and sufficient 

 ammonia to account for the alkaline reaction sometimes ob- 

 served is produced. 



CORRELATION OF OTHER CHARACTERS WITH THE GAS RATIO 



The " Methyl red test." It has been shown by Michaelis 

 and Marcora 7 that the growth of a colon culture ceases when 

 a certain hydrogen ion concentration is reached. This re- 



c L. V. Burton and L. F. Rettger, Correlations in the Colon-Aerogenes 

 Group in Jour. Inf. Dis., 21, 2, pp. 162-195, 1917. 



7 L. Michaelis and F. Marcora, Die Kiinerproduktivittit des Bacterium 

 Coli in Ztschr. f. ImmnnitiitsforscJi. u. exper. Therap., Grig., 14, 2, pp. 

 170-173, 1912. 



