HANDLING HOG CHOLERA IN THE FIELD 163 



place while passive immunity due to serum alone 

 still exists, a permanent immunity is acquired; 

 if it takes place after the passive immunity dis- 

 appears, the animal will readily contract hog 

 cholera; and, except where hogs are quite closely 

 confined, chance alone must decide whether any 

 particular individual will become permanently im- 

 mune, or, failing in this, eventually die of hog 

 cholera. 



Method number two will produce more reliable 

 results. The sick are distinguished from the well 

 by physical appearance and temperature read- 

 ings. In handling herds in this manner it is our 

 custom to give serum alone to all animals showing 

 temperatures above 104 F., and to all visibly sick, 

 and not at the point of death, regardless of tem- 

 perature reading. If, however, the weather is 

 warm, and if the hogs are excited in handling, 

 most temperatures will rise above this point, and 

 the thermometer gives us very little information. 

 Under such circumstances physical appearance is 

 our only guide. A useful practice, whenever con- 

 ditions are such that it can be employed, is to feed 

 the hogs a little grain and to place those that leave 

 the feed in a few moments among the sick that are 

 to receive serum alone, and those that remain for 

 a longer time and eat greedily, among the well 

 that are to receive serum and virus. Practically 

 all will eat a little, but the infected animals are 



