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BUBONIC PLAGUE.                       441

the influence of sunlight and desiccation cannot be relied
upon to limit its viability.

Kitasato's experiments first showed that it is possible
to bring about immunity to the disease, and Yersin,
working in India, and Fitzpatrick, in New York, have
successfully immunized large animals (horses, sheep,
goats). The serum of these immunized animals con-
tains an antitoxin capable not only of preventing the dis-
ease, but also of curing it in mice and guinea-pigs and
probably in man.

Haff kine in his experiments followed the line of pre-
ventive inoculation as employed against cholera. Bouil-
lon cultures were used in which floating drops of butter
were employed to make the islands of plague bacilli
float. The cultures were grown for a month or so, suc-
cessive crops of the island-stalactite growth as it formed
having been precipitated by agitating the tube. In this
manner there was obtained an " intense extracellular
toxin" containing large numbers of the bacilli. The
culture was killed by exposure to a temperature of 70
C. for one hour, and the mixture used in doses of about
3 as a preventive inoculation. In the Byculla
Gaol, where Haff kine's experiments numbered over one
hundred, a decided prophylactic effect was observed in
twelve to fourteen hours in men already advanced in the
stage of incubation.

Wyssokowitz and Zabolotmy, whose studies have
already been quoted, used 96 monkeys in the study of
the value of the t( plague-serums," and found that
when the treatment is begun within two days from the
time of inoculation the animals can be saved, even
though symptoms of the disease are marked. After the
second day the treatment cannot be relied upon. The
dose necessary was 20 of a serum having a potency
of i : 10. If too little serum was given, the course of
the disease was slowed, the animal improved for a time
and then suffered a relapse, and died in from thirteen to
seventeen days. The serum also produced immunity,