METHODS OF USING AN TI- HOG- CHOLERA SERUM 127 



The practicing veterinarian is regularly re- 

 quired to select the method best suited to the 

 conditions he encounters, and he can handle hog 

 cholera with maximum efficiency only when he 

 judiciously chooses and employs the particular 

 method indicated. The selection is based entirely 

 on the effects produced by each method, just as we 

 choose drugs on the basis of their action. When 

 once these effects are well understood, the choice 

 involves no great difficulties. 



Serum alone method. This consists of deep 

 injection of the required quantity of serum. If 

 the animals thus treated are not infected l with 

 hog cholera immediately before or during the four 

 weeks following serum administration the immu- 

 nity conferred may, with rare exceptions, be de- 

 pended on four weeks. In many individuals it 

 lasts much longer. Swine more than twelve weeks 

 old that receive serum alone and are infected with 

 cholera immediately before immunization, or dur- 

 ing the three or four weeks following, are there- 

 after permanently immune. The effect on pigs 

 less than twelve weeks old is still a matter of con- 

 troversy, but at present we are not safe in depend- 



1 Much misunderstanding has arisen because of the loose use 

 of the terms "infected" and "exposed." The first term implies 

 that hog cholera virus sufficient to produce the disease has actually 

 entered the system; the second implies that the animal has been 

 in close contact with virus from any source, but infection may 

 or may not have taken place. Hogs given serum alone and in- 

 fected with hog cholera acquire a permanent immunity; if they 

 are exposed but not actually infected the immunity is temporary. 



