infectious material becoming scattered about the premises, leaving a centre
of infection in the neighborhood and causing outbreaks of cholera among
neighboring herds. It may be advisable to burn the corn-cobs and other
litter that have accumulated about the yards. Loose board floors should be
torn up and the manure from beneath removed. Portable houses should be
removed. The floors, walls of the house and fences should be first cleaned
by scraping off the filth, and then sprayed with a three per cent water
solution of a cresol or coal tar disinfectant to which sufficient lime has
been added to make a thin whitewash. Three or four months of warm, sunny
weather are sufficient to destroy the cholera infection in well-cleaned
yards.

ANTI-HOG-CHOLERA SERUM.--The credit of developing the first and at present
the only reliable anti-hog-cholera serum and method of vaccination belongs
to Drs. Dorset and Niles. Anti-hog-cholera serum came into general use in
1908, and all of the swine-producing States have established State
laboratories for the production of this serum.

Anti-hog-cholera serum is produced by injecting directly, or indirectly,
into the blood-vessels of an immune hog a large quantity of cholera virus,
secured by bleeding a hog that is fatally sick with acute cholera, and
bleeding the injected animal after it has completely recovered from the
injection. The injection of the cholera blood is for the purpose of
stimulating the production of antibodies by the body tissues, and raising
the protective properties of the immune hog's blood. An animal so treated
is called a hyperimmune (Fig. 85). The blood from the hyperimmunes is
defibrinated and a preservative added, and after it has been tested for
potency and freedom from contaminating organisms, it is ready for use.

[Illustration: FIG. 85.--Hyperimmune hogs used for the production of