396 The Diseases of Animals 
meters, and the cost per average-sized dose will be 
about twenty-five cents. Most states have laboratories 
that supply the serum at cost. 
Owing to the cost of serum, it may not be practical 
to vaccinate hogs in regions where the disease rarely 
occurs; but in regions where the disease is frequent, or 
when the disease appears in a locality, or in animals 
that are liable to exposure to the infection, the serum 
should be used. 
The serum is not only a preventive of hog cholera, 
but assists in curing animals when used in the early 
stages. In vaccinating a herd, the sick animals should 
be left until the last, to avoid possible spread of infec- 
tion by the vaccinating instruments. The serum is 
injected with a hypodermic syringe, and full directions 
ean be obtained with the serum. 
Hog cholera seems to be caused by an “ultra-micro- 
scopic” germ, or one so small that it cannot be seen by 
the most powerful modern microscopes; consequently 
a rigid quarantine should be maintained against per- 
sons, as well as animals, from infected places. 
The germs of hog cholera are scattered about by the 
discharges from sick animals as they are moved over 
the country. When hogs are shipped in cars, the latter 
become infested; hence, the necessity of thoroughly 
disinfecting cars before shipping healthy hogs in them. 
Streams are frequent sources of infection; it is common 
to find the disease occurring at farm after farm in 
succession along a watercourse. The writer has seen 
the bodies of hogs floating down streams during out- 
breaks of cholera. Sick hogs are likely to wander 
