TECHNIQUE OF THE VOGES AND PROSKAUER REACTION 497 



ages of positive Voges and Proskauer reactions in the two con- 

 tainers showed a marked disagreement. 



4. Based on the nmiiber of positive Voges and Proskauer 

 reactions, Clemesha's medium ranks first, the glucose potassium 

 phosphate medium second when inoculated at 37.5°C. for forty- 

 eight hours, and third when inoculated at 30°C. for five days. 



In the course of this study it became evident that a consider- 

 able number of organisms would give positive Voges and Pros- 

 kauer reactions with Clemesha's medium and negative results 

 with the glucose potassium phosphate medium. Furthermore 

 the latter, when inoculated with the same culture, did not always 

 yield positive Voges and Proskauer reactions after incubation 

 at 30°C. for five days and 37.5°C. for two days. In seeking an 

 explanation for this non-agreement the influences of temperature 

 and incubation period were studied by inoculating large quanti- 

 ties of glucose potassium phosphate broth and Clemesha's me- 

 dium with various cultures so that portions could be removed 

 for testing the Voges and Proskauer reactions at twenty-four hour 

 intervals for a period of five days. It was found that: forty- 

 eight hours' incubation was sufficient time for the develop- 

 ment of acetyl-inethyl-carbinol and a longer incubation period 

 exerted an unfavorable influence. In general, the intensities of 

 the colors which developed after the addition of sodium hydroxide 

 diminished as the incubation period increased, faint and very 

 faint pink colors appearing and shading, in some cases, to brown 

 or yellow. At the end of forty-eight hours colors of a uniform 

 strong pink shade appeared and doubtful colors were absent. 

 A considerable percentage of cultures yielded positive Voges and 

 Proskauer reactions at the end of twenty-four and forty-eight 

 hours and negative at the end of five days. Table 3 contains 

 the results of some tests made to illustrate the influence of the 

 period of incubation on the development of positive Voges and 

 Proskauer reactions. From each 100 cultures tested by the 

 Voges and Proskauer reaction 'the tests indicated were obtained 

 in the respective media at the various incubation periods. 



Table 2 shows that cultures in Clemesha's medium incubated 

 at 37.5°C. for two days yield a larger percentage of positive 

 Voges and Proskauer reactions (see columns headed ''Dish" — 



THE JOURN VL OF BACTERIOLOGY, VOL. III. ND. 3 



