Section IV., 1915 [207] Trans. R.S.C. 



A Study of some Organisms which produce black fields in 

 Aesculin-hilesalt media. 



By F. C. Harrison and J. Vanderleck, Macdonald College, P.Q. 

 (Read May Meeting, 1915). 



In the summer of 1913 samples of milk obtained from more 

 than a thousand different dealers or farmers in the province of Quebec 

 were analysed. Nine plates were made from each sample — 3 aesculin- 

 bilesalt-agar plates (Note 1); 3 litmus-beef-peptone-lactose agar 

 plates; and 3 beef-peptone-litmus-lactose gelatine plates. 



A large number of colonies were selected from all of the above 

 plates to test the reliability of aesculin-bilesalt-agar plates for the 

 identification of the colon-aerogenes group. These colonies may be 

 grouped as follows: — 



Selection 1. Colonies producing black or brown fields on aesculin 

 plates. 

 " 2. Colonies producing very faint black or brown fields 



on aesculin plates. 

 " 3. Colonies, resembling those of the colon-aerogenes group 

 on the aesculin plates, but failing to produce coloured 

 fields. 

 " 4. Colonies on litmus-lactose agar resembling those of the 



colon-aerogenes group. 

 " 5. Colonies on litmus-lactose agar resembling those of the 

 colon-aerogenes group but producing neutral or alkaline 

 fields. 

 All agar plates were incubated at 37 °C. for 48 hours, and counted. 

 As a rule, these plates were at once cleaned, but a few were kept at 

 room temperature for several days and from these a number of atypical 

 colonies were isolated. 



Over 600 pure cultures were isolated from the plates for further 

 study, and all were transferred to tubes of sterile htmus milk (Note 2) 

 and incubated at 37 °C. After 24 hours 214 tubes showed strong 

 gas production and acidity without coagulation. These tubes were 

 presumed to contain cultures of the colon-aerogenes group. As a 

 further safeguard 61 tubes were selected at random and transferred 

 to the usual test media. Without exception, the tested cultures be- 

 longed to the colon-aerogenes group. 



The 214 cultures, mentioned above, were plated again on aesculin- 

 bilesalt agar and all produced the characteristic black or brown 



