A Study of the B. coli Group. 
359 
1 2 3 4 5 
0-2 per cent. 0-3 per cent. 0*4 per cent. 0 5 per cent. 07 per cent. 
On all these plates abundant growths were obtained and all the colonies 
were of the large type. A subcultivation was again made on ordinary agar 
from plate 5 and from this plates containing the acid in still higher pro- 
portions were inoculated. 
12 3 
0-5 per cent. . 1 per cent. . 2 per cent. 
Growth was abundant on plates 1 and 2 ; in the case of plate 3 the 
growth was slower in appearing, but ultimately a few" large colonies developed. 
Thus a monochloracetic acid resistant strain was selected out, and subcultures 
on ordinary medium when tested were found to produce acid only from, 
glucose, acid and considerably reduced amount of gas from lactose and 
galactose, acid and gas (in a slightly reduced amount) from dulcite and 
mannite. 
A similar test was carried out with a sub-group A type 1 strain ; the 
selected strain capable of growing on 2*5 per cent, monochloracetic acid agar 
showed also absence of gas production in glucose, considerably reduced gas 
production in lactose and galactose, and slightly reduced gas production 
from dulcite and mannite. Other strains of typical B. coli and a B. proteus 
were tested with similar result as regards the particular sugars of the above 
series fermented. 
The results diifered from those of Penfold* in that the only " sugar " (of 
2 monosaccharides, a disaccharide and 2 hexahydric alcohols) from which 
these variants completely failed to produce gas was glucose, though in the 
case of lactose and galactose there was some depression of the gas-producing 
property. 
All these variants maintained their stability as regards the new character 
even after several months' subculture on ordinary agar, but by subculturing 
every day in glucose peptone water for a week, a reversion of the strain was 
noted and the power of producing gas was regained. Harden and Penfold 
found that, from the biochemical standpoint, the change was more a quanti- 
tative than a qualitative one. 
Thus from my observations it was only possible to completely abolish the 
gas production of B. coli in the case of glucose, and it was also shown 
that the original character could be easily regained under certain conditions. 
It was in no way possible to select from an aerogenes B. coli type a corre- 
sponding anaerogenes variety. 
The absence of gas production after several subcultures may, therefore, 
be regarded as a fundamental character of certain coliform types. 
* Penfold's variant strains showed absence of gas production in lactose as well as 
o'lncose. 
