It also very soon takes on a somewhat granular appearance.
As the colony increases, the granular character becomes more marked, until
it seems to be made up of highly refractile granules, like a mass of
particles of glass. In its further growth the gelatine is liquefied in the
vicinity of the colony, which at the same time sinks down deeper into the
gelatine mass, and makes a small thread-like excavation in the gelatine,
in the center of which the colony appears as a small white point. This
again is peculiar; it is never seen, at least so marked, with any other
bacterium. And a similar appearance is produced when gelatine is
inoculated with a pure culture of this bacillus, the gelatine liquefying
at the seat of inoculation, and the small colony continually enlarging;
but above it there occurs the excavated spot, like a bubble of air
floating over the bacillary colony. It gives the impression that the
bacillus growth not only liquefies the gelatine, but causes a rapid
evaporation of the fluid so formed. Many bacteria also have the power of
so liquefying gelatine with which they are inoculated, but never do they
produce such an excavation with the bladder-like cavity on the surface.
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