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Scientific Memoirs by
That such a relation may exist even between Bacilli is well known, and a
very striking example of it has presented itself during the current year in the
Laboratory in Calcutta. In it the relation has advanced so far as to come to be
one of actual commensalism, or perhaps rather of parasitism, in so far as
one of the associated species of Bacilli is concerned. The favouring or host-
species was apparently merely the common Hay-Bacillus, and was readily
susceptible of pure cultivation. The other was a much smaller, slender form
in which the rods were either isolated or associated in filamentous fashion.
The rods and filaments are in themselves colourless, but their presence in any
cultivation of the Hay-Bacillus is soon revealed by the gradual development of
a red tint passing on gradually into a splendid scarlet. When first observed
the growth manifested itself spontaneously in connection with a cultivation
of the Hay-Bacillus derived from a sample of blood which had been obtained
from a supposed case of anthrax. Here, after the cultivation was some
days old, and when the surface of the gelatine was covered by a thick,
yellowish stratum of the Hay-Bacillus, a bright scarlet, shining patch some
-what elevated above the surrounding surface, and contrasting beautifully
with it, made its appearance. This gradually spread, and ultimately the
entire surface of the Hay-Bacillus became of the same scarlet hue. Very
many attempts have been made to procure pure cultivations of the intrusive
species, but always in vain. Plate-cultivations have yielded pure growths of the
Hay-Bacillus, and so have tube-cultivations inoculated from others in which
the mixed growth is at an early stage of development. The latter fact is due to
the very different rates of growth of the two species when they are simultaneous
-ly introduced to a new medium. Even where the inoculating material is
derived from tubes of long duration, and in which the elements of the Hay-Bacillus
are only present in relatively very small numbers and in a condition of evident
extreme involution, a yellowish halo of them in pure, or almost pure, condition
almost invariably manifests itself around the scarlet point of the inoculation, and
by inoculating from this area in one or two successive cases a stage is arrived at
in which the yellow growth alone makes its appearance and retains the character
of a pure cultivation permanently. The difference in the rate of growth of the
two Bacilli is, to a considerable extent, due to the fact that the medium alone
is necessary for the growth of the Hay-Bacillus, while that of the other species
is dependent on the pre-existence of its companion. That this is so comes out
very clearly in cases where a tube which has become occupied by a large growth
of the Hay-Bacillus as the result of previous inoculation is inoculated with the
material of a mixed growth of long duration in which the other species is present
in excess; for in such cases red colouration very rapidly manifests itself over
large areas, in place of spreading slowly over the surface in the track of its host.
The relation between the two species would appear to be one rather of true
parasitism than of commensalism, for there can be no doubt that the growth of the