MANUFACTURE OF HOG-CHOLERA SERUM 333 



cently given the simultaneous or double treatment. In such ani- 

 mals there is produced a permanent type of active immunity, as a 

 result of which these hogs can be given enormous doses of hog- 

 cholera virus without any effect other than stimulation of the 

 production of antibodies. 



In these cases where it is not easy to secure hogs that have 

 already received the simultaneous treatment, the next best plan is 

 to secure a number of swine and inject them by the double method. 

 In this way immunity is produced, and we have a herd of our own 

 ready for use. This last plan has one disadvantage, in that it will 

 be necessarj" to wait for a few weeks before beginning the process of 

 hyperimmunization. In serum plants where check pigs are used 

 to test serum the pigs that are treated by simultaneous method in 

 testing out the potency of the serum can be kept, and allowed to 

 run in pasture for several weeks until they reach the necessary 

 size to make their use for serum production profitable. In this 

 manner a constant supply of immune hogs will be on hand after the 

 first few months the plant is in operation. 



Some serum manufacturers who are afraid of or opposed to the 

 double method of treatment produce immune hogs by giving a 

 dose of serum to a number of hogs, and then turning them into a 

 pen that is infected with cholera virus by the presence of hogs 

 sick with the disease. This method is a little uncertain, as all of the 

 hogs so treated may not develop a permanent type of immunity. 

 The most certain and the most economic method of securing im- 

 munes is by injecting as many as are needed by the double or 

 simultaneous method. It is necessary to wait for at least twenty- 

 one days after giving of this double treatment before further injec- 

 tions are given for the purpose of producing the condition known as 

 hyperimmunity. This wait is necessary in order to give the cells 

 of the body time in which to accustom themselves to the work of 

 manufacturing the needed antibodies with which to withstand the 

 enormous doses of virus blood that are to be given later on. 



Source of Virulent Blood. — As the next step in the process of 

 serum manufacture it is necessary to inject into the body of these 

 immune hogs a large dose of virulent blood. This virus blood con- 

 tains an enormous amount of the germs or virus that produces 

 hog-cholera, and the object of the injection is to stimulate the 



