334 DISEASES OF SWINE 



cells of this animal's body to the production of the highest possible 

 number of antibodies. The means of obtaining this virus blood 

 is the biggest problem in the manufacture of hog-cholera serum, 

 and many solutions have been offered. 



Stock-yard Virus. — The easiest means of securing virus is by 

 sending men to the slaughtering plants where hogs are killed, or 

 make some arrangements with the proprietors of these slaughtering 

 plants to secure the blood from all animals killed that are suffering 

 from cholera. Where this is done, the usual plan is to take these 

 hogs that show signs of cholera when received in the stock-yards, 

 and when they are killed the blood from them is saved and in- 

 jected into the immune hogs for the purpose of producing cholera 

 serum. In some cases an effort is made to observe these animals 

 after slaughter and examine them for lesions of cholera. 



This plan is the cheapest way out of the difficult problem, but 

 it is also the least desireable. Virus obtained in this manner is 

 always of questionable potency, and very often is drawn under 

 conditions that do not tend to furnish a product that is free from 

 contamination with other germs as well as the germs of cholera. 

 This is a very important matter. The purity and strength of the 

 virus is of the most extreme importance in determining the quahty 

 of the serum that will result. Low-grade virus means a low-grade 

 serum, and this means poor results when the serum is used in the 

 field. 



In the manufacture of hog-cholera serum it is desirable that we 

 obtain a virus of the highest possible disease-producing power. 

 The more powerful or virulent the virus, the more pronounced 

 will be the reaction on the part of the tissue cells. This means 

 more antibodies, and the more antibodies that are formed, the more 

 potent will be the serum that results. In using a slaughter-house 

 virus we have no means of determining whether the virus present 

 is of a powerful grade or of a low type of disease-producing quality. 

 Where it is desired to produce the highest possible quality of 

 serum this means of securing virus should not be considered. 



Field Virus. — Another method of obtaining virus blood for 

 hyperimmunization purposes is to draw blood from those animals 

 which are first attacked at the beginning of an outbreak. It has 

 been found that the virus of cholera is always apparently a little 



