MANUFACTURE OF HOG-CHOLERA SERUM 



357 



known in the serum trade as " rehyperimmunization " or " re- 

 hypering." 



There is some question as to just how soon this should be done. 

 At several plants they make four bleedings from the tail before 

 again injecting with virus. This was formerly the practice in the 

 United States Government Serum Laboratory, but they are now 

 prefering to reinject with virus after the third bleeding. There is 

 some question as to whether or not it does interfere with the 

 strength of the serum to make more than three bleedings. The 

 safer plan would seem to be to adhere to the three-bleeding policy. 



Fig. 66. — Filtering hog-cholera serum to remove clot (Tennessee State Serimi 

 Plant). 



Handling of Serum Blood. — As soon as the tail bleeding has 

 been stopped the blood which has been drawn is treated in very 

 much the same manner as that just described for handling of virus 

 blood. The drawn blood is quickly shaken or placed in a shaking 

 machine and the clot-forming material removed. It is then strained 

 through a cotton filter, so as to remove any foreign material or 

 shreds of clot. 



This filtered fluid is received into large clean bottles which have 



