[HARRISON- ORGANISMS IN AESCULIN-BILESALT MEDIA 209 



vanderleck] 



Of the 87 tubes of G, 22 have black fields on aesculin plates. 

 These organisms were obtained from selection 1. The remaining 

 65 colonies were from selections 3 and 4. 



The 55 tubes of H, showing various changes were plated on aescu- 

 lin agar. After 48 hours' incubation at 37 °C. 4 plates developed 

 black colonies. When the remaining plates were kept at room temper- 

 ature for 6 days, 7 more developed black colonies. These eleven plates 

 were further investigated. 



The 37 tubes collected under K and L had no importance; they 

 produced colourless colonies on the aesculin plates. Altogether 17 

 colonies were left for further investigation, viz., 6 from Group E and 

 11 from Group H. Some of these as mentioned above took consider- 

 able time to develop black colonies on the aesculin plates. These 

 cultures behaved on aesculin as follows: — 



Cultures, 125, 171, 174, 175, 293, 358 made black colonies at 

 37°C. in 24 hours. 



Cultures 109, 294, 381, 441 made black colonies at 37°C. in 48 

 hours. 



Cultures 336, 300, 304, 314, 338, 437, 600 did not produce coloured 

 colonies at 37 °C. in 4 days, but produced black colonies at 

 20°C. in 7 days. 



These cultures would not have appeared in the usual routine 

 examination of the milk, but they are included here because they 

 have been mentioned by other investigators as impairing the reliability 

 of aesculin media as a test for the colon-aerogenes group. 



We may add that many of the 600 colonies were selected because 

 they seemed to be slightly atypical, and yet we found that there were 

 only 10 exceptions, a percentage of 1-5 of all the colonies tested, and 

 a percentage of 0-03 of the colonies on the plates from which these 

 600 were isolated. 



