364 DISEASES OF SWINE 



they show well-marked symptoms of cholera and their blood drawn 

 in the usual manner for use as virus for hyperimmunizing other 

 larger hogs. This means a saving in expense, as by this means 

 the same shoats can be used for checks and virus pigs. For this 

 reason it is a good plan to use 4 check pigs instead of 2, and in 

 nearly all serum plants the plan of using 4 check pigs is followed. 

 This gives the same number unprotected as protected. Some men 

 also give the same dose of virus to the check pigs as to those that 

 are treated with serum. 



This is the only real method of proving whether or not a serum 

 is active in its power to protect against cholera. Every batch of 



Fig. 67. — Dead check pig in serum test. Other pigs protected by serum 

 remained healthy (H. K. Mulford Co.). 



serum should be tested in this manner before being sent into the 

 field, and any serum which is not capable of protecting the 100- 

 pound shoat from a 2-c.c. dose of virus when given in dosage of 

 30 c.c, and even in dose of 15 c.c, should be rejected. In like 

 manner, no virus should be sent out for use in the field unless it has 

 been tried out on check pigs and found to be capable of producing 

 the disease. It is absolutely necessary that both serum and virus 

 be active if the desired results are to be obtained from the simul- 

 taneous or double method of treatment. 



Preparation of Virus for Field. — Virus blood that is intended to 

 be shipped into the field for use in giving the double method of 



