TECHNIQUE OF THE \OGES AND PROSKAUER REACTION 495 



of the two media with 283 strains of lactose fermenting organisms 

 which were negative to methyl red. The development of the 

 pink color was noted at the end of 1, 2, 5, and 20 to 25 (over 

 night) hours after the addition of 0.5 cc. of a 45 per cent solution 

 of sodium hydroxide to the tubes of Clemesha's medium and 5 cc. 

 of a 10 per cent solution to the tubes of glucose potassium phos- 

 phate medium. The positive reactions are expressed in per- 

 centages of the 283 methyl red negative organisms. 



From this table it is seen that the correlation percentages 

 are much higher in the case of Clemesha's medium; that the 

 five hour period of reaction with the sodium hydroxide is the 

 optimum interval of time for the development of the pink color; 



TABLE 1 



Percentages of positive Voges and Proskauer reactions with 283 methyl red negative 



reactions 



and that the over night period gives erroneous results on account 

 of the fading of the pink color. All tubes in which a noticeable 

 pink color developed were called positive. Part of the negative 

 tubes were colorless and part were characterized by a yellowish 

 green color. 



From the work of Harden and Walpole it appeared that oxida- 

 tion plays an important part in the development of the pink color. 

 In order to hasten the oxidation the more intimate exposure of a 

 portion of the incubated culture appeared to be the next step 

 in the investigation. Accordingly Syracuse watch glasses 

 measuring 5 cm. in diameter by 8 mm. in depth were employed 

 as containers. In such a dish 1 cc. of liquid is spread over an 

 area of about 20 sq. cm. with a resulting depth of liquid of about 



