154 HOG CHOLERA 



action and consequent permanent immunity due 

 to subsequent serum-virus treatment. The im- 

 pression seems to prevail that there is just one 

 way to immunize a hog permanently, and that is 

 to give him simultaneous treatment as a first and 

 only measure. Various troubles following follow- 

 up treatment have been cited as proof of this 

 theory, but we have never investigated a case in 

 which there was the least evidence that the system 

 was fundamentally at fault. The trouble has been 

 in its application. 



In applying the follow-up system, there is a 

 marked tendency for the veterinarian to give the 

 dose of serum alone and to neglect for too long a 

 time to follow it with simultaneous treatment. 

 There is no danger in this unless the pigs happen 

 to be exposed to cholera after the passive immu- 

 nity due to the dose of serum has disappeared, 

 but too often just that very thing takes place. The 

 owner of the animals derives a false sense of se- 

 curity from the fact that serum has been adminis- 

 tered, and hence does not report the sickness as 

 promptly as he otherwise would. The final result 

 is that when hog cholera is well started in the 

 herd, the veterinarian receives an urgent call to 

 give serum and virus as the final installment of 

 the follow-up treatment. Heavy losses inevitably 

 follow, and the entire system is condemned. It 

 should always be remembered that serum alone 



