330 DISEASES OF SWINE 



these large additional doses of disease-producing material that the 

 number of antibodies contained therein had been materially in- 

 creased. This was a very important discovery. The degree of 

 protection that the blood offers against invasion by the germs is in 

 direct proportion to the number of antibodies to be found in the 

 serum obtained from it. If, therefore, we are able to increase the 

 number of antibodies by injection of more germs after the animal 

 has developed an immunity, we are able to produce an animal that 

 has even greater protective power than that possessed by the regu- 

 lar immune hog. This condition of high-degree immunity is known 

 as hyperimmunity, and the animal having a protective power of 

 this high standard is known as a hyperimmune. The injection of 

 virus material to produce this condition of hyperimmunity is 

 known as hyperimmunization. 



This is the essential process in the manufacture of what is known 

 as hog-cholera serum, as we shall find when we take up the consid- 

 eration of the method of producing this very valuable therapeutic 

 agent. It is the blood from hyperimmune hogs which is taken 

 for use in protecting other hogs against the attacks of the hog- 

 cholera virus. By the process of hyperimmunization the formation 

 of enormous numbers of the germ-destroying antibodies is encour- 

 aged, and the blood from one of these animals is, accordingly, a very 

 powerful protective agent in the defense against attack by the 

 virus of the disease. 



Summary.— In considering the manner of production of im- 

 munity the following interesting facts are worthy of reconsidera- 

 tion: 



(1) Immunity is the result of the presence in the blood of a large 

 number of germ-fighting bodies which are known as antibodies. 



(2) These antibodies are formed by the cells of the animal 

 body as a result of an actual attack by germs or virus of disease. 



(3) Once the cells of the body acquire the knowledge of how 

 these antibodies are formed, and the important part they play in 

 defense against disease, they never neglect to keep a plentiful sup- 

 ply on hand. As a result, the body is always prepared to resist a 

 second attack by these same germs. 



(4) The antibodies are not damaged by withdrawal of the blood 

 from one animal and injection into the body of another animal of 



