192 THE FARMER S VETERINARIAN 



skin; (3) by injecting virulent blood in smaller 

 doses directly into the blood circulation. 



In this work an ordinary immune hog weighing 

 loo pounds is given a quart of very virulent blood. 

 a teaspoon of which similarly injected would kill 

 a hog that was not immune. In other words the 

 immune, and especially the hyperimmune hog, have 

 developed certain properties in their blood antago- 

 nistic to hog cholera virus. 



Vaccination. We have two possible methods of 

 vaccinating or immunizing susceptible hogs (a) 

 Serum only. This is by the injection under the 

 skin of serum from the body of a hyperimmune hog 

 and gives immediate but temporary immunity last- 

 ing, as already stated, several weeks. If this animal, 

 during the period of immunity, is exposed to 

 natural infection, he becomes protected for a very 

 long period, perhaps for life, (b) Simultaneous. 

 The second method of vaccination consists of in- 

 jecting immunizing blood serum into one thigh and 

 a small amount of disease-producing serum at the 

 same time, or soon after, into the other thigh, thus 

 giving the animal the cholera and a cure for it at 

 the same time. If the immunizing serum is potent 

 and the virulent serum is really virulent, then the 

 animal so treated becomes permanently immune. 



The serum-only method is usually preferred in 

 actual outbreaks and for hogs not yet sick, because 

 this gives immediate protection, and the hogs, being 

 naturally exposed, usually develop a permanent im- 

 munity. The simultaneous method of vaccination 

 is preferred where we are very confident of the 

 serum's potency against the virulent blood, and for 

 hogs that have not yet been infected. It may yet 

 be found wise to use this method even in out- 

 breaks. 



