31 



2. The reaction may be obtained after 14 to 24 hours incubation at 

 30 degrees or 37 degrees C. 



3. The brand of peptone employed does not affect the intensity of 

 the reaction. 



It is interesting to note that in case of a mixture of coli and aerogenes 

 types, the methyl red test will be acid and the V. P. reaction will be 

 positive. Undoubtedly many instances are recorded as examples of inter- 

 mediate strains when they were really due to impure cultures. This was 

 the experience of Johnson and Levine who found that by repeated puri- 

 fication, the proportion of strains which would not show perfect correlation 

 was considerably reduced. Chen and Rettger record that of 18 strains 

 which persisted in giving methyl red positive and V. P. positive reactions 

 in all media, which they employed, only four continued to give non-corre- 

 lating reactions after purification, although contaminating organisms could 

 not be demonstrated. 



Resume. The gas ratio, Voges Proskauer, methyl red, and uric 

 acid tests are strikingly correlated. The members of the colon group 

 which produce acetyl methyl carbinol, are capable of using the nitrogen 

 from the purin ring of uric acid, give an alkaline reaction with the methyl 

 red test, and in the decomposition of glucose, yield a relatively small 

 quantity of acid and two or more times as much C0 2 as H 2 . On the 

 other hand, the organisms, which do not produce- acetyl methyl carbinol, 

 can not utilize the nitrogen from the purin ring, give an acid reaction with 

 methyl red, break down glucose with the production of a relatively large 

 amount of acid and liberate C0 2 and H 2 in approximately equal volumes. 

 The colon group therefore includes two distinct subdivisions which are 

 characteristically of different sources. These have been designated the 

 coli and aerogenes sections. Their characteristics are tabulated below: 



TABLE XIV. DIFFERENTIATION OF THE MAIN SUBDIVISIONS OF THE 



COLON GROUP. 



