one very
forcibly of the spirochaete of relapsing fever. Indeed, it would be
difficult to distinguish the two if placed side by side. On account of
this developmental change, he doubted if the cholera organism should be
ranked with bacilli; it is rather a transitional form between the bacillus
and the spirillum. Possibly it is a true spirillum, portions of which
appear in the comma shape, much as in other spirilla--_e. g_., spirilla
undula, which do not always form complete spirals, but consist only of
more or less curved rods. The comma bacilli thrive well in meat infusion,
growing in it with great rapidity. By examining, microscopically, a drop
of this broth culture the baccilli are seen in active movement, swarming
at the margins of the drop, interspersed with the spiral threads, which
are also apparently mobile. They grow also in other fluids--_e. g_., very
abundantly in milk, without coagulating it or changing its appearance.
Also in blood serum they grow very richly.

Another good nutrient medium is gelatine, wherein the comma bacilli form
colonies of a perfectly characteristic kind, different from those of any
other form of bacteria. The colony when very young appears as a pale and
small spot, not completely spherical as other bacterial colonies in
gelatine are wont to be, but with a more or less irregular, protruding, or
jagged contour. 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 ar