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fermentation tube contains gas, it is most probable that bacillus coli communis
is present; if, on the other hand, the fluid has changed into red, but the
fermentation tube contains no gas, then it is quite clear that at this stage,
i.e., after 24-48 hours' incubation, the bacillus coli communis is absent, but
a microbe may be present belonging to the coli-typhoid group, since
MacConkey fluid (taurocholate) hinders, or at least retards most microbes
other than those of the coli-typhoid group.
Those MacConkey tubes which, after 24 hours' incubation at 37° C.,
were red and had no gas were used for establishing (f) further surface phenol
agar plates and the primary phenol broth tube (a) above-mentioned, belonging
to the same set as these MacConkey tubes, were likewise used for
establishing (g) further phenol gelatine plates. The primary phenol agar
plate and phenol gelatine plate (d and e), after incubation (d at 20-21° C.,
(e) at 37° C.), were carefully examined, and those colonies which resembled
those of the coli-typhoid group were examined microscopically, and of
them sub-cultures were made in the different media used for identifying
bacillus coli communis, bacillus of Gaertner, or bacillus typhosus. In the same
manner, from the secondary plates (f and g) sub-cultures were made of
doubtful or suspicious colonies. These sub-cultures were: gelatine streak
and gelatine shake cultures, ordinary broth, litmus milk, flagella staining, if
necessary, and finally tests with blood of a typhoid immunised guinea-pig
kept for the purpose; this blood having been ascertained to agglutinate
emulsion of the true typhoid bacillus at 1 in 100, or even 200, within 20-25
minutes.
It will, from the foregoing, be understood that the amount of work
and the number of cultures used were very extensive, and this must be
in the nature of the thing, since nowadays the identification as bacillus
typhosus of a microbe belonging to the coli-typhoid group is justly
considered unsatisfactory unless the above tests all come out satisfactorily.
To examine on this scale, then, a dozen oysters is a work of considerable
complexity, and above all, work which requires a great deal of
time. In addition to the above cultures of one dozen oysters, I have
examined a further half-dozen by litmus lactose phenol Agar or by litmus
glycose Agar plates : on incubation the colonies of bacillus coli become
noticeable by being surrounded by red medium, due to rapid acid production,
whereas those of bacillus typhosus are in blue medium, this microbe
not being able to produce acid so rapidly, or fermenting lactose.
The result of the above cultures and sub-cultures was this:—
(1.) Every one of the eighteen oysters examined contained
bacillus coli communis.
(2.) Three out of the eighteen oysters contained, in addition, a
variety of bacillus coli which differs from the bacillus coli
communis by the cylindrical form and the great mobility of
the bacilli; by its not forming indol in broth and not curdling
milk; by its not fermenting lactose; the bacilli are covered
with many thin, long spiral flagella. From these characters
it is clear that this variety belongs to the Gaertner-typhoid