A Study of the B. coli Group. 
357 
In tlie C sub-group all the strains tested exhibited a high resistance to 
brilliant green, equal to that shown by the mutating strains of sub- 
group B. 
In the D sub-group there was some variation in the susceptibility of 
different types, but the number of strains available for testing was too 
limited to draw any inferences from the results. 
These findings correlated with the serological observations are of con- 
siderable interest ; from the serological study it was concluded that the gas 
+ , indol + , inosite — types could be grouped together apart from the other 
organisms of the B. coli group. The tests carried out with these organisms 
growing on brilliant green media also show the striking distinction between 
organisms of the sub-group A on the one hand and the C types and also 
certain of the B types on the other. 
While the A types (with few exceptions) are all more or less similar in 
their behaviour, and the same is also true for the C types, various B and D 
types behave differently. 
In the B sub-group the lactose-fermenters were differentiated sero- 
logically from the paracolon varieties and those which only fermented lactose 
after mutation; in the brilliant green resistance tests a corresponding- 
difference was established. 
These experiments, therefore, apart from the practical bearing they had 
in connection with the brilliant green enrichment process for the isolation of 
B. typhosus, were of considerable interest in correlation with the previous 
work on tlie classification of the B. coli group. 
. VARIATION AMONG THE COLIFORM BACILLI. 
Variation in Gtas Production. 
Among these organisms certain anomalies have been noted as regards 
this property (Mair, Wilson and others) ; thus strains when first isolated 
may show complete absence of gas production, but on repeated subculture 
develop this property. Reference has already been made to strains of 
paracolon bacilli (p. 329) which in primary culture simulated B. typhosus in 
their cultural reactions. The possibility of this variation must be considered, 
therefore, in the practical identification of intestinal bacilli. A B. para- 
typhosus A in the first cultures made after isolation may show complete 
absence of gas production, and if it only ferments dulcite slowly, as is often 
tke case, it may thus simulate B. typhosus in cultural characters. B. clysen- 
teriae Shiga may also be simulated by a non-motile organism which after 
repeated subculture ferments glucose with gas production, though in primary 
culture it produces no gas (of glucose, lactose, dulcite, saccharose, mannite, 
maltose, only glucose fermented). 
