136 
cannot be considered complete unless the organism is 
isolated in pure culture, and is found to show the following 
characters :—Typical morphology, 7.e., a non-sporing bacillus 
relatively small and often quite thick ; motility, when a young 
growth on gelatine culture is examined ; non-liquefaction of 
gelatine ; fermentation of glucose broth, with the formation 
of about 50 per cent. of gas of which about } (CO,) is absorbed 
by 2 per cent. solution sodium hydrate ; coagulation of milk 
with the production of acid in 48 hours or more at 37° C., 
either spontaneously or on boiling ; production of indol in > 
peptone solution ; reduction of nitrates. 
(3) Houston describes ‘‘ Coli communis ’’ as follows :— 
The organism is motile; gives gas in gelatine shake cultures ; 
acid and gas in both glucose and lactose peptone media ; 
positive result with neutral red broth; indol formed ; acid 
and clot in litmus milk ; gas acid and clot in lactose peptone 
milk cultures ; reduction of nitrates ; bright cherry red colour 
in Proskauer and Capaldi medium No. I; bleached appear- 
ance and no definite acidity in Proskauer and Capaldi medium 
No. II; percentage acidity in litmus whey culture == 28 to 
46.£:6; IN. 10, Na,CO,, 
(4) Savage gives the following tests as both essential and 
sufficient to identify true bacillus coli communis for purposes 
of water analysis. A short bacillus with rounded ends; no 
spores ; motile ; decolourized by Gram’s method ; character- . 
istic growth on gelatine slope; acid production and coagu- 
lation in litmus milk; production of indol; production of 
considerable quantity of acid in litmus whey ; fermentation 
with production of both gas and acid in glucose and lactose 
media ; no fermentation in starch or saccharose ; a positive 
neutral red reaction. 
From the work previously described it is certain that 
(1) Houston’s true coli is not a single organism at all but a 
group of some ten or a dozen bacilli, and (11) there is an enor- 
mous number of bacilli—such as the saccharose fermenters— 
in feces that must be called ‘‘ atypical coli,’’ because they 
only partially fulfil the above conditions. 
It would appear that this arrangement of classifying feecal 
bacilli into ‘‘ true coli ’’ and ‘‘ atypical coli’’ is open to 
+) 
