Another peculiarity was the slowness with which the gelatine liquefied,
and the narrow limits of this liquefaction in the case of a gelatine disk.
Cultures of the comma bacillus were also made in agar-agar jelly, which is
not liquefied by them. On potato these bacilli grow like those of
glanders, forming a grayish-brown layer on the surface. The comma bacilli
thrive best at temperatures between 30 deg. and 40 deg. C., but they are not very
sensitive to low temperatures, their growth not being prevented until 17 deg.
or 16 deg. C. is reached. In this respect they agree with anthrax bacilli.
Koch made an experiment to ascertain whether a very low temperature not
merely checked development but killed them, and subjected the comma
bacilli to a temperature of 10 deg. C. They were then completely frozen, but
yet retained vitality, growing in gelatine afterward. Other experiments,
by excluding air from the gelatine cultures, or placing them under an
exhausted bell jar, or in an atmosphere of carbonic acid, went to prove
that they required air and oxygen for their growth; but the deprivation
did not kill them, since on removing them from these conditions they again
began to grow.
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