41 2 PA THOGENIC BACTERfA.

Pasteur discovered that when cultures are allowed to
remain undisturbed for several months, their virulence
is greatly lessened, and new cultures planted from these
are also attenuated. When chickens are inoculated with
such cultures, no other change occurs than a local in-
flammatory reaction by which the birds are protected
against virulent bacilli. From this observation Pasteur
worked out a system of protective vaccination in which
fowls can first be inoculated with very weak, then with
stronger, and finally with highly virulent cultures, with
a resulting protection and immunity. Unfortunately,
the method is too complicated to be very practical. Use
has, however, been made of the ability of this bacillus
to kill rabbits, and in Australia, where they are pests,
they are being exterminated by the use of bouillon cul-
ture. It is estimated that two gallons of bouillon culture
will destroy 20,000 rabbits irrespective of infection by
contagion.

The bacillus of chicken-cholera seems not only to be
specific for that disease, but seems able, when properly
introduced into various other animals, to produce several
different diseases. Indeed, no little confusion has arisen
in bacteriology by the description of what is now pretty
generally accepted to be this very bacillus under the
various names of bacillus of rabbit-septicemia (Koch),
Bacillus cuniculicida (Fliigge), bacillus of swine-plague
(Loffler and Schiitz), bacillus of iC Wildseuche" (Hiippe),
bacillus of l' Biiffelseuche " (Oriste-Armanni), etc.