HANDLING HOG CHOLERA IN THE FIELD 175 



in the negative we should advise the breeder not to 

 immunize. It is an unnecessary expense, and 

 when once simultaneous treatment is employed 

 in a herd there is some danger in discontinuing 

 its use. Pigs thus immunized may eliminate vir- 

 us, and this may be on hand to infect susceptible 

 animals that subsequently are added to the herd 

 by birth or purchase. In case it is desired to dis- 

 continue immunization, at least four months, and 

 preferably six, should elapse between the date 

 when simultaneous treatment is last used on the 

 place, and that of the introduction of susceptible 

 recruits into the herd. All of these facts should 

 be perfectly clear to the breeder before virus is 

 used in his herd. 



When chances of infection with hog cholera are 

 remote, and the breeder is advised against main- 

 taining an immune herd, he should be cautioned 

 against all the practices that may result in the in- 

 fection of his swine. He should also be informed 

 regarding the things that would lead him to sus- 

 pect the presence of hog cholera, and the neces- 

 sity for early reporting of an outbreak, should it 

 occur, must be made plain. 



When hog cholera threatens ultimately to attack 

 a herd and destroy it we can render the breeder 

 no greater service than in advising him to main- 

 tain it immune to cholera. Much as we dislike the 

 idea, in the abstract, of introducing virus into 



