362 DISEASES OF SWINE 



serum turned out is of a clear, yellowish color, making a much more 

 elegant-appearing product, and one that is much more conve- 

 niently handled. 



In the United States the use of the centrifuged or clear serum 

 has never seemed to meet with a great amount of general favor. 

 There have been a number of objections raised to the removal of 

 these red blood-cells. The most important of these, perhaps, is the 

 fact that it materially adds to the cost of the process of manu- 

 facture. It is, accordingly, not regarded as advisable, in view of 

 the fact that the price of serum is already so high as to in part 

 hinder its use. 



Another and even more serious objection has been raised, in 

 that there is a possibility of decreasing the potency of the serum 

 when we remove from it these same red blood-cells. No extensive 

 experiments are on record as yet in this direction, but several ob- 

 servers have offered the suggestion that the germ-destroying anti- 

 bodies may be in large part carried in the red blood-cells. This is a 

 point worthy of serious consideration, although results with the use 

 of other serums do not seem to bear out this theory. 



For the present, however, the cost of removal of the red blood- 

 cells is such as to make it inadvisable to add so materially to the 

 expense of production by use of a procedure that is of questionable 

 value. 



Testing of Serum. — Before any batch of serum is sent out into 

 the field for actual use it should be submitted to severe experimen- 

 tal tests on living shoats at the serum plant. This experiment is 

 carried out in very much the following way: 



First a number of pigs or young shoats are secured that will 

 average about 60 to 100 pounds each. These are divided into 

 several small lots of 2 each. In one lot of 2 an injection is 

 given with 2 c.c. of virus blood and 15 c.c. of the serum. Another 

 group of 2 pigs is injected with 2 c.c. of virus blood and 30 c.c. 

 of serum. A third group of 4 pigs is injected with 1 c.c. of the 

 virus alone. 



In both the first and the second groups an injection has been 

 given of double the usual fatal dose of virus blood. Under ordi- 

 nary conditions this amount of the same blood would destroy the 

 life of these animals in seven to ten days. If they are to be saved 



