208 THE ROYAL SOCIETY OF CANADA 



fields. These fields differed according as they were surface or deep 

 colonies and as they represent all the various types of colonies found 

 in the colon-aerogenes group, their appearance and descriptions are 

 given in Plate I. 



These 214 cultures were originally obtained as follows: — 

 177 were selected from aesculin plates. All produced black or brown 



fields. These belong to selection 1. 

 37 were selected from litmus-lactose-agar plates, as resembling typical 



colon-aerogenes colonies. These belong to selection 4. 



The remaining 384 milk tubes were incubated again for 24 hours 

 at 37°C. and were then sorted as follow: — 



A. 16 tubes, strong gas production, acid, without coagulation. 



B. 94 tubes, strong gas production, acid and coagulation. 



C. 7 tubes, strong gas production, coagulation and complete re- 

 duction of the litmus. 



D. 12 tubes, gas production, alkaline without coagulation. 



E. 32 tubes. Alkaline. 



F. 56 tubes, alkaline and marked digestion. 



G. 87 tubes. Acid without coagulation. 



H. 55 tubes. Various changes not mentioned above. 

 K. 27 tubes. No change in milk, although bacteria were demon- 

 strated in large numbers. 

 L. 10 tubes. No bacteria could be found in spite of repeated 



re-inoculations. 



The tubes mentioned under A, B and C, 16, 94 and 7 in number 

 were plated on aesculin-bjlesalt agar. 



Only black or brown colonies developed. All these cultures were 

 isolated from the original aesculin-bilesalt-agar plates. It was inter- 

 esting to note that the cultures of B and C formed, as a rule, large 

 brown slimy colonies surrounded by a brown field, and it is probable 

 that these organisms belonged to the aerogenes type. These 117 

 organisms were considered to belong to the colon-aerogenes group. 



The 12 tubes of D gave white colonies without field when plated 

 on aesculin agar, and were originally from selection 5. 



The 32 tubes of E were plated on aesculin agar and to our surprise 

 six showed a heavy slimy growth, with large dark brown field, and 

 would have been taken for aerogenes colonies. 



The dark brown colonies on these six plates were isolated and re- 

 inoculated into litmus milk, and produced the alkaline reaction 

 already mentioned. These six cultures had been obtained under 

 selection 1, and the remaining 26 under selection 5. 



The 56 tubes of F plated on aesculin-bilesalt-agar did not produce 

 coloured fields and were the colourless colonies of selection 3. 



