856 
TREATMENT OF SWINE DISEASES. 
The production of a certain degree of immniiity by inocula¬ 
tion and by vaccination has been a favorite method of combat¬ 
ing several of the destructive contagious diseases of animals 
and has been extensively tried with swine diseases, as was ex¬ 
plained in the preceding article. In experimenting with inocu¬ 
lation it was discovered that a comparatively small quantity of 
the blood of an immune animal, if injected into the tissues of a 
susceptible animal, would produce immunity in the latter and 
would also, in case the animal was suffering from the disease, 
have a curative effect. 
This was a most wonderful and unexpected discovery, which 
has been particularly utilized for the cure and prevention of 
diphtheria in the human species. It is a principle capable of 
quite general application, however, and seems particularly use¬ 
ful for the control of the prevailing outbreaks of swine diseases. 
It has the great advantage over inoculation and vaccination in 
the field that it does not distribute the germs and consequently 
cannot produce outbreaks of disease nor can it injure the animal 
in any manner. 
In practice it is found convenient to draw the blood of the 
immune animal, allow it to clot or coagulate, and then to re¬ 
move the liquid portion of the serum for use. The application 
of this liquid to the prevention or cure of disease is, therefore, 
called the serum treatment. 
In producing this serum on a large scale it is necessary to 
use large animals which can furnish a considerable quantity of 
blood at one time without seriously affecting their condition. 
For* this reason horses and cattle are favorite animals with 
which to produce such serums. To make a horse immue to 
hog cholera or swine plague it is first inoculated with a very 
small dose of the germs of one of these diseases. This inocula¬ 
tion is follpwed by the symptoms of depression and fever, which 
vary in intensity and duration according to the size of the dose 
and the susceptibility of the animal. After the horse has en¬ 
tirely recovered from the effects of this inoculation it has ac¬ 
quired a slight degree of immunity, but its blood does not yet 
show any appreciable immunizing or curative properties. To 
develop^ such properties the animal must be inoculated again 
and again, with an ever-increasing dose of virus until the high¬ 
est practicable degree of immunity is obtained. After each 
inoculation the horse must be allowed to recover entirely from 
its effects before another inoculation is practiced. 
It requires from three to four months of the most careful 
