PREPARATION OF ANTI-HOG-CHOLERA' SERUM 109 



ease (heavy ascaris infestation) necessitated 

 three retests which were satisfactory, one 10 mil 

 serum pig died in each of two, one 15 mil pig died 

 in one, and two were wholly unsatisfactory due to 

 low potency. The test pigs ranged in weight be- 

 tween 27 and 105 pounds, the average being 59. 



It is of advantage to select test pigs from herds 

 in which no immunizing has been done and in 

 which hog cholera has not appeared in recent 

 years. It is well if all pigs in a single test can 

 be litter mates. The pigs should not be subjected 

 to long hauls just before they go on test, and dur- 

 ing the test great care is necessary to prevent 

 overfeeding of the serum pigs at the time when 

 their reaction begins, which is about the time the 

 virus pigs refuse feed entirely. As a routine 

 measure it is a good plan to reduce the feed one- 

 third or one-half on the morning of the fourth day 

 of test, and to feed subsequently so that the serum 

 pigs are kept just a little hungry. 



It is interesting and highly instructive to ob- 

 serve the progress of a series of tests, and we 

 know that some field workers would be more cau- 

 tious in their vaccinating if this experience could 

 be theirs. It is in this manner that we see results 

 of the battle between protective and destructive 

 forces, and are brought to realize how easy it is 

 for some disturbing factor to turn the tide in 

 favor of destruction. The virus pigs usually show 



