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Transactions of the Boyal Society of South Africa. 
and this also differentiated these organisms from the lactose-fermenting 
types. 
The Comparative Eesistance to Brilliant Green of Different 
Types or Coliporm Bacilli with Reference to the 
Classification of these Organisms. 
In the course of certain observations on the enrichment of B. tyjjhosus 
by culture from faeces in fluid media containing brilliant green (Browning, 
Grilmour and Mackie), it was noted that different types of B. coli exhibited 
different degrees of susceptibility to this chemical. The " typical " varieties 
(sub-group A, types 1, 2, 3, etc.) were completely inhibited in their growth 
on culture medium by concentrations of brilliant green which had no effect 
on B. typhostis, but it was noted that the inosite fermenters (sub-group 
C) on the contrary exhibited a resistance to the dye greater even than 
that of the typhoid bacillus. 
As this appeared to be a striking difference between two B. coli sub- 
groups already classified separately on an entirely different basis, there 
seemed some likelihood that the study of the behaviour of different coliform 
types towards this dye might throw some further light on the biological 
relationships of the various cultural types. 
For this purpose a series of representative strains from the four sub- 
groups were tested as regards the inhibition of their growth in peptone- 
water-agar by different quantities of brilliant green incorporated in the 
medium. 
The concentrations of the dye tested were 0*16, 0*22, 0 32, 0*42 c.c. of 
a 1 : 10,000 watery solution in 10 c.c. of the medium. 
Emulsions of the various organisms were made in sterile salt solution, of 
such density that the fluid showed a mere trace of turbidity to the eye, and 
cultures were made by taking one loopful of the emulsion and spreading it 
on the medium in stroke form (one stroke only). On ordinary medium this 
inoculation produced an abundant line of growth along the needle tract. 
One plate was, of course, used to accommodate several strokes from different 
organisms. 
The plates were incubated for forty-eight hours and readings were made 
after twenty-four and forty-eight hours. 
With two exceptions all the sub-group A organisms tested proved 
relatively susceptible (as compared with B. typhosus) to the dye, including 
non-lactose-fermenters (Table XXVIII) ; the exceptions were (1) a strain of 
type 9 and (2) a strain of type 22 (isolated from a case of conjunctivitis) ; 
another strain of type 9, however, corresponded in its behaviour to the other 
A types. It is noteworthy that these two strains also differed in the com- 
plement-deviation experiments from other A types. 
