INFECTIOUS DISEASES 203 



eighty or ninety percent of the exposed herd. The serum 

 alone is recommended for immunizing pregnant sows, 

 because the simultaneous method frequently produces 

 abortion. This method should also be used to immunize 

 swine that are to be introduced into healthy, susceptible 

 herds. 



The dose of the serum in the serum-alone treatment 

 should not be less than thirty cubic centimeters for each 

 hundred-pound live weight of hog. 



The simultaneous method is used more extensively 



Fig. 23. CHOLERA-IMMUNE HOGS. 



There is a firm at the Stock Yards in Chit-ago manufacturing anti-hog 

 cholera serum that makes & business of vaccinating* hogs, that are 

 to be kept in the Yards, at $1.00 per hundred pounds and guarantee- 

 ing the owners against loss. These hogs are kept in the Yards from 

 three weeks to two months and are driven about from pen to pen 

 to clean up the feed left by other animals. They are of course 

 continually exposed to virulent infection. 



than the serum alone, because it produces a longer im- 

 munity. The dose of serum used in the simultaneous 

 method should be fifty percent more than the dose in the 

 serum-alone method. The serum and virus must be in- 

 troduced separately in different parts of the body. 



This method may be used successfully in exposed 

 herds, especially in those swine that do not show a high 

 temperature. But the virus should not be given to hogs 

 that are showing visible signs of cholera. 



The one serious disadvantage of the simultaneous 

 method is the fact that infection is introduced. Good 



