734 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



or " quick" method. In the former, now seldom used, the animals 

 receive several injections at intervals of every few days, each succeeding 

 dose being increased in proportion to the weight of the animal. In the 

 "quick" method the virus is injected in one large dose, the amount being 

 determined by the weight of the animal. The virus may be injected 

 intramuscularly, intraperitoneally or intravenously, the latter method 

 now being used almost exclusively. Ten days to two weeks after the 

 hyperimmune hog has received the last injection of virus, the animal 

 is ready for bleeding. When bled from the tail, the end of the appen- 

 dage is severed with a sharp instrument, several hundred cubic centi- 

 meters of blood are collected aseptically, defibrinated, a preservative 

 added and the material placed in the refrigerator. This process is 

 repeated several times, at intervals of one week to ten days, when the 

 animal is ready for final bleeding. 



By this procedure all the blood is secured from the animal according 

 to the method described for bleeding virus pigs. The "slaughter" 

 method, used in many laboratories, consists of only the final bleeding, 

 thus eliminating tail bleedings. As a rule the different lots of serum 

 representing the different bleedings from several hyperimmune hogs 

 are mixed and the whole subjected to test. In order to test the 

 potency of the product eight susceptible pigs, each weighing about 23 

 kg. (50 pounds) are inoculated subcutaneously, each with 2 c.c. of 

 virus. Six of these pigs are simultaneously injected with graduated 

 doses (15 to 25 c.c.) of the serum under test. If the hyperimmune 

 serum possesses potency the test pigs should remain in a normal con- 

 dition throughout the test, except for the presence of thermal reactions 

 and slight clinical symptoms, while the two control pigs should show 

 severe symptoms in five or six days and should die in less than 

 fifteen days. 



The practical method of treatment in the field consists in the simul- 

 taneous injection of the hyperimmune serum and virus (double treat- 

 ment), into healthy hogs for the purpose of immunization. The 

 amount of hyperimmune serum which should be injected varies from 

 30 c.c. to 90 c.c., depending upon the weight of the hog to be treated. 

 Thus, a hog weighing 34 kg. to 45 kg. (75 to 100 pounds) usually receives 

 40 c.c. of serum, together with i c.c. of virus. The usual dose of virus 

 for hogs above 34 kg. (75 pounds) weight is 2 c.c. For pigs weighing 

 less than 23 kg. (50 pounds) J^ c.c. of virus should be injected. 



