332 



DISEASES OF SWINE 



regard for cleanliness. The watchwords for success in manufacture 

 of serum are carefulness and cleanliness. With this motto the man- 

 ufacture of hog-cholera serum is a comparatively simple process. 



Immune Hogs Necessary. — The first essential in the manu- 

 facture of serum is to secure some immune hogs with which to 

 start. The main point in preparing serum is the production of a 

 blood that contains an enormous number of germ-fighting bodies, 

 and this can only be done where we have immune hogs that are 



Fig. 56. — Virus operating room in State Serum Plant at Nashville, Tenn. 

 Giving intravenous injection of virus for production of hyperimmunity. 



capable of receiving large doses of virulent blood without harmful 

 effect. 



In securing these immune hogs there are two principal sources 

 of supply. One means is to secure hogs that have passed through 

 an attack of cholera and have been left with an acquired immunity. 

 This source of supply is, however, very limited, and, as such ani- 

 mals are highly prized for breeding purposes, the expense would be 

 almost prohibitive. 



The better method is to purchase animals that have been re- 



