260 



CHEN CHONG CHEN AND LEO F. RETTGER 



many instances motility could be detected without any difficulty, 

 it was at times very difficult to reach a satisfactory conclusion. 

 The following table summarizes the results. 



Motility 



TYPES OF ORGANISMS 



B. coli 



B. aerogenes. 



NUMBER 



EXAMINED 



173 



447 



ACTION ON CASEIN, GELATIN LIQUEFACTION AND INDOL 

 PRODUCTION 



The reaction of the different strains in litmus milk was more 

 or less uniform at the end of the observation period, namely 

 seventy-two hours. Some difference was observed, of course, in 

 the rapidity with which visible acid production was brought 

 about; but with few exceptions all of the strains turned the litmus 

 red and coagulated the casein within seventy-two hours. In 

 the exceptional instances application of heat was necessary to 

 bring about the coagulation. 



Gelatin liquefaction was determined by the two following 

 methods. In the first, tubes of nutrient gelatin were inoculated 

 (stabbed) with a twenty-four hour agar culture and incubated 

 at 20°C. for six weeks. Observations were made at the end of 3, 

 7, 14, 21, 39 and 42 days. In the second method, a loopful of a 

 twenty-four-hour broth culture was spread over the surface of 

 standard nutrient gelatin and incubated at 37°C. for thirty days. 

 At the end of five-day intervals the tubes were placed in the refrig- 

 erator. Tubes in which no liquefaction was demonstrable were 

 returned to the incubator. The results obtained by both methods 

 are given in the following table. 



The superiority of the 37° method is clearly brought out here. 

 According to this, 17 of the aerogenes strains were liquefiers. 

 None of the coli cultures possessed this property. 



