IMMUNITY—ANTITOXINS. 
the disease is starved out. Sometimes the action 
of the germs upon the cells of the body produces 
a condition which is poisonous to the germs them¬ 
selves and thus they are destroyed by the pro¬ 
ducts of their own vital activities. In either 
case the tissues are left in a state of immunity 
from that particular disease for a longer or 
shorter period, sometimes for life. We are told 
of three forms of immunity. 
I. —Natural immunity, which is the natural and 
constant resistance of the antagonistic cells or 
phagocytes to the development within the body of 
pathogenic bacteria. 
II. —Acquired immunity, which is that immun¬ 
ity given to the body, or which the body 
gains, by a single attack of a certain commun¬ 
icable disease. 
III. —Artificial immunity, which is that immun¬ 
ity given to, or gained by the body, through the 
use of antitoxins. 
Antitoxins are antidotes to bacterial poisons. 
These substances are obtained by injecting into 
the body of one of the lower animals, found sub¬ 
ject to the disease, poisons produced by patho¬ 
genic bacteria while developing in broth, bouillon 
or other culture media. After the bacteria have 
remained in the culture media for a stated period 
their poison permeates it. Some of the bouillon 
is then taken and injected into the chosen animal 
(horses, goats, guinea pigs, rabbits, etc., are all 
experimented upon. The horse is preferred for 
the development of diphtheria antitoxin), with a 
special syringe, in very small doses at first which 
are gradually increased until the animal ceases to 
37 
Immunity. 
Natural 
Immunity. 
Acquired 
Immunity. 
Artificial 
Immunity. 
Antitoxins. 
