through the
agency of dogs, wolves, buzzards, or crows, the disinfection of the stables
and the ground where the animals lay at the time of death, and, if
possible, the destruction of the germs on the infected pastures. One of the
most effective methods for freeing an infected pasture from blackleg is to
allow the grass to grow high, and when sufficiently dry to burn it off. One
burning off is not sufficient to redeem an infected pasture, but the
process should be repeated several years in succession. This method,
however, is in many instances impracticable, as few cattle owners can
afford to do it, and the only means left for the protection of the animals
is vaccination.

_Immunization by vaccination._--Three French veterinarians, Arloing,
Cornevin, and Thomas, were the first to discover that cattle may be
protected against blackleg by inoculation with virulent material obtained
from animals which have died of this disease. Later they devised a method
of inoculation with the attenuated or weakened blackleg spores which
produced immunity from natural or artificial inoculation of virulent
blackleg germs. Their method has undergone various modifications both in
regard to the manufacture of the vaccine and in the mode of its
application. Kitt, a German scientist, modified the method so that but one
inoculation of the vaccine was required instead of two, as was the case
with that made by the French investigators. The vaccine formerly prepared
and distributed by the Bureau of Animal Industry combined the principle of
Arloing, Cornevin, and Thomas, and the modification of Kitt.

By vaccination we understand the injection of a minute amount of
attenuated--that is, artificially weakened--blackleg virus into the system.
This virus is obtained from animals which have died from blackleg, by
securing the affected muscles, cutting them into strips, and drying them in
the air. When they are perfectly dry they are pulverized and mixed with
water to form a paste, smeared in a thin layer on flat dishes, placed in an
oven, and heated for six hours at a temperature close to that of boiling
water. The paste is then transformed into a hard crust, which is pulverized
and sifted and distributed in packages containing either 10 or 25 doses.
This constitutes the vaccine, the strength of which is thoroughly tested on
experiment animals before it is distributed among the cattle owners. This
vaccine, which is in the form of a brownish, dry powder