HOG CHOLERA 283 



even up to four days after exposure. Thus it is seen that 

 a considerable number of hogs of a herd may be saved 

 even after the disease breaks out. The entire number 

 would probably not be exposed at the beginning, and fur- 

 thermore, the disease is not transipitted from one indi- 

 vidual to the next in the herd until after it breaks out, 

 and there is a period of incubation between the time the 

 hog is exposed and the time the disease breaks out or 

 manifests itself. Thus after the disease appears in visible 

 form in a herd, if the healthy individuals are immediately 

 inoculated, a greater portion of them may be saved. In 

 such a case, the simple method of inoculation by using the 

 protective serum alone, and not the virulent hog cholera 

 serum, will furnish practically the same results in the in- 

 dividuals that were already exposed as would otherwise 

 be obtained where the entire healthy herd is treated by 

 means of the serum simultaneous method ; because after 

 being exposed to the disease, the hog has already in his 

 system the virus or the germs that produce the disease, 

 the same as would be introduced by injecting into the hog 

 the two or three c. c. of virulent hog cholera serum. The 

 protective serum that is injected at such a time will coun- 

 teract the disease germs that are already in the system 

 and thus render the hogs more or less permanently im- 

 mune, at least for a period of several months. 



Objections to the Serum Method of Treatment. — ^The 

 two principal objections to this method of treating hogs 

 to protect them from hog cholera are that it is expensive, 

 and that it is somewhat dangerous. It is expensive be- 

 cause a hog will furnish a comparatively small amount of 

 blood, from 1000 to 2000 c. c, from which the serum can 

 be obtained. Considering that the clot must be taken 

 from this, and that it requires from 20 to 30 c. c. for a 



