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BACTERIA.                              35


highly-refracting sphere or ovoid situated in a little col-
lection of granular matter.

Spores differ from the bacteria in that their capsules
seem to prevent evaporation and to enable them to with-
stand drying and the application of a considerable amount
of heat. Ordinarily, bacteria are unable to resist a tem-
perature above 60 C. for any considerable length of
time, only a few resistant forms tolerating a temperature
of 70 C. The spores, however, are uninjured by such
temperatures, and can even successfully resist that of
boiling water (100 C.) for a short time. The extreme
desiccation caused by a protracted exposure to a tem-
perature of 150 C. will, however, destroy them. Not only
can the spores resist a considerable degree of heat, but
they are also unaffected by cold of almost any intensity.

While the cell-wall of the bacterium is easily pene-
trated by solutions of the anilin dyes, it is a matter of
much difficulty to accomplish the staining of spores, so
that we see they are probably more resistant to the
action of chemical agents than the bacteria themselves.

When a spore is accidentally dropped into some nu-
trient medium a change is shortly observed. The proto-
plasm, which has been clear, becomes somewhat granu-
lar, the capsule a little less distinct; the body increases
slightly in size, and in the course of time splits open to
allow the escape of the young organism. The direction
in which the escape of the young bacillus takes place is
of interest, as varying in the different species. The
Bacillus subtilis escapes from the end of the spore, where
a longitudinal fissure occurs; the bacillus of anthrax
escapes from the side, sometimes leaving the capsule of
the spore in the shape of two small cups.

As soon as the young bacillus escapes it begins to in-
crease in size, develops around its soft protoplasm a cha-
racteristic capsule, and, having once established itself,
presently begins the propagation of its species by fission.

In addition to the endospores, of which we have just
been speaking, there .are arthrospores. The formation