330 BUILDINGS, SANITATION, AND DISEASES 
s 
Immunization.—To the investigations of the Bureau of 
Animal Industry of the U. 8. Department of Agriculture, we 
are indebted for the production of a serum which seems likely 
to play an important part in the suppression of hog cholera. 
Briefly, the serum is prepared from the blood of hogs treated in 
such a way as to render them immune from the disease. The 
Ai 2 ET a 
Courtesy Tennessee Department of Agriculture. 
Fic, 94.—Injecting serum into muscle of ham (pig). 
serum: is injected under the skin of healthy hogs which it is 
desired to protect from the disease. (Figs. 93, 94, 95.) It 
is not a cure for cholera, but is wholly preventive in character, 
bearing the same relation to hog cholera as vaccine bears to 
smallpox. 
In an address before the American Veterinary Medical 
