452 FARM ANIMALS 
of action especially for this class. Indeed, it is far easier to under- 
stand the simple laws of prevention than complicated curative proc- 
esses. Especially is this true after germs become known and iso- 
lated, and their rapid destruction by air, sunlight and disinfectants 
understood and available. 
6. Immunity by inoculation—Many diseases are fre- 
quently combated by introducing into the blood a certain 
serum that enables the body to resist attack 
of that disease. Immunity in animals in- 
cludes both natural and acquired powers 
which the body possesses to destroy bac- 
teria and poisons. The serums or inocu- 
lating materials are carefully prepared in 
laboratories by using treated blood of other 
animals; when prepared the desired serum is 
injected under the skin. Thus immunity is 
secured in the animal so treated. A few of 
the many diseases now treated by inocula- 
InocuraTinc tHe tion are tetanus, Texas fever, hog cholera, 
Hoc WITH 
Serum ror Diack leg, anthrax and diphtheria. Each is 
Ceyae’ °F a very destructive disease, and unless 
treated by inoculation, a large percentage of 
afflicted animals never recover. If, however, animals are 
inoculated before being attacked by the disease, the loss 
from death is relatively small. 
7. Some animals resistant to disease—An infectious 
or contagious disease may inflict a herd or flock and de- 
stroy few or many of the individuals composing it. Some 
animals are never affected, although subjected to expo- 
sure and contagion. Such animals are immune and resist 
that particular disease. Others may suffer a mild attack 
and throw it off with no disastrous consequences; these 
are strong and their organs ably fortified against any 
injurious inroad from that disease. On the other hand, 
most animals are not able to throw off disease. Their 
