154 MAX LEVINE 



The real significance of the accurately determined gas ratio 

 was not appreciated until 1914 when Rogers called attention 

 to the striking correlation between this ratio and the source 

 of the organisms. In three papers by Rogers, Clark and Davis, 

 (1914) and Rogers, Clark and Evans (1914 and 1915), it is 

 demonstrated quite conclusively that fecal strains of B. coli 

 (at least those derived from bovine feces) break down glucose 

 with the liberation of carbon dioxide and hydrogen in about 

 equal volumes, while non-fecal (grain) strains form two or 

 more times as much carbon dioxide as hydrogen. The sanitary 

 significance of such a division is evident, but the accurately 

 determined gas ratio is inapplicable to routine work. 



Clark and Lubs (1915) note that the gas ratio is correlated 

 with the H+ ion concentration and that the difference in H+ ion 

 concentration between the low and high ratio groups is such 

 that it may be easily recognized by methyl red. When grown 

 in appropriate glucose media the low ratio, (fecal) group is 

 acid and the high ratio (non-fecal) group alkaline to this indicator. 



As no earlier investigators employed the methyl red reaction, 

 the valuable work of these men cannot be compared directly 

 or adequately with former investigations, unless some previously 

 employed test is found which is well correlated with either the 

 gas ratio or the methyl red test. The Voges-Proskauer reaction 

 seems to serve this purpose. 



THE VOGES-PROSKAUER REACTION 



The chemistry of the Voges-Proskauer reaction has been 

 worked out in detail by Harden and his associates in England. 

 West refers to one of Harden's articles in which it is pointed 

 out that the reaction is due to the production of acetyl-methyl- 

 carbinol and urges that this test be studied further, as it is of 

 considerable importance in recognizing B. aerogenes and B. 

 cloacae. Among other investigators who have employed this 

 reaction in studies on B. coli may be mentioned, Durham, Mac- 

 Conkey, Rivas, Bergey and Deehan, Ferriera, Horta and Paredes, 

 Copeland and Hoover, Clemesha, Archibald and more recently 

 Khgler and Levine. 



