102 IOWA DEPARTMENT OF AGRICULTURE 
to the same disease. These two facts; the presence of the filtered virus 
in the blood of hogs sick of hog cholera and the immunity in hogs which 
have recovered from an attack of the disease form a basis for the prepara- 
tion of the serum which we have used successfully in immunizing hogs 
againsL hog cholera. 
He says that the protective serum is produced by a process of Hyper- 
immunization carried out as follows: An immune hog is injected with 
large amount of blood from hogs sick of hog cholera. This injection will 
not produce more than a transitory effect upon the health of the immune 
although they would prove certainly fatal to a susceptible hog. This 
treatment of immune hogs with large amount of disease producing blood 
is known as hyper-immunization and gives to the blood of the immune the 
power to protect susceptible hogs from hog cholera. In about a v.-eek or 
so after the immune has recovered from the effect of this treatment, blood 
is drawn from the immune by cutting off the tail. The blood drawing is 
repeated three or four times at intervals of a week between drawings, 
after which the immune is usually bled to death from the carotid. 
After each drawing from the immune the blood obtained is defribri- 
nated and mixed with a suitable antiseptic. If preserved in sterile bot- 
tles this defribrinated blood, or serum as it is called, will retain its 
potency indefinitely. The protective serum having been obtained from 
an immune hog in the manner indicated, the potency of this serum is 
determined by injecting susceptible hogs with varying amounts of this 
serum and at the same time exposing them to hog cholera along with 
untreated or controlled animals. In practice it will, of course, be found 
best to first collect large quantities of serum and to mix this before test- 
ing. A standard serum will thus be secured at a minimum cost. This 
serum having been secured, either of two methods may be used for pro- 
tecting susceptible hogs. These are known as (A), the serum simultan- 
eous method, and (B), serum alone me. nod. 
The first of these, which is to be recommended for use especially in 
herds which have not been exposed to hog cholera, consists in injecting 
subcutaneously on one side of the body of the hog lo be vaccinated, a 
suitable quantity of serum and simultaneously on the other side of the 
body a small quantity of virolent blood taken from a hog sick of hog 
cholera. 
Experience has shown that by this method hogs are given a firm im- 
munity lasting at least six months and probably much longer. 
The serum alone method, which consists simply of the injection of the 
protective serum without the simultaneous use of disease producing blood, 
appears to confer only a temporary immunity upon the treated hogs, un- 
less they be exposed to hog cholera a short time after receiving the 
serum. In which case they also acquire a lasting immunity. For these 
reasons, the serum alone method is admirably adopted to the treatment 
of hogs in a herd where hog cholera has already broken out, but which 
have not themselves shown visible symptoms of the disease. It should 
be stated, that either method when properly applied will not injure the 
hog in any way. 
