A SfMcly of the B. coll Group. 
823 
Litmus lias been frequently used as an indicator of acid formation, but 
with this agent, especially when incorporated in nutrient medium, difficulties 
have frequently arisen owing to the many intermediate degrees of colour 
between unequivocal alkalinity on the one hand and undoubted acidity on 
the other. It has the further disadvantage, as I have noted, of being 
decolorised rapidly b}^ many organisms of the coll group. In my own 
experience neutral red is a more valuable indicator as it is not subject 
to these disadvantages. 
System of Classification and Designation Adopted. 
Among the coliform bacilli studied, it seemed possible to classify into 
separate sub-groups, types of organisms having well-defined common 
characters. 
Thus the different types which were characterised by the absence of gas 
production in the case of all the sugars fermented even after repeated sub- 
culture {coli anaerogeues) were classified in a separate sub-group. Serological 
investigations (v. infra) in which the group action of the complement- 
deviating antibody of immune sera to certain more typical B. coli varieties 
showed that the coli ariaerocjenes organisms were not closely related to the 
gas-producing types of B. coli. 
It was also noted that certain types of coliform bacilli which produced on 
culture medium unusually large, thick, opaque, slimy and sometimes " viscid " 
colonies were all characterised by possessing the power of fermenting iiiosite 
while the usual B. coli varieties had not this property. These organisms 
were therefore grouped together and classified apart from the more typical 
coliform bacilli. All these varieties proved to be non-motile, all fermented 
lactose, saccharose, raffinose and salicin, and with one exception adonite ; in 
this sub-group therefore several characters were definitely correlated. The 
separation of these organisms from the typical coliform bacilli was also found 
to be justified by serological tests as in the case of the anaerogeues sub-group. 
It was further concluded from the serological studies referred to above, 
and dealt with in detail later, that a sub-group comprising all the " typical 
B. coli " could be recognised whbse common characters were — gas-producing, 
indol-forming, noii-inosite-fermenting. 
After defining these three sub-groups, there still remained the organisms 
having the common characters— gas-producing, non-inosite-fermenting, iion- 
iiidol-formiiig. Serological observations showed that this category did not 
represent a serologically homogeneous sub-group, but for purposes of a pre- 
liminary classification I have grouped all the organisms of the category 
together. 
Thus four main sub-groups of the Gram-negative, glucose-fermenting, 
non-gelatin-liquefying intestinal bacilli may be recognised and this system 
of classification has been used in the following records. In addition, the 
