136 HOG CHOLERA 



they occur in the hams of hogs ready for market 

 they are highly objectionable, as they cause con- 

 demnation of the entire quarter in which they are 

 located. The handling of vaccination abscesses 

 consists of opening them when the first evidence 

 of fluctuation appears, pressing out the thick, 

 greenish-yellow pus which they usually contain, 

 and irrigating the sac with weak antiseptic solu- 

 tion. In opening, the incision should be made with 

 due regard for continuous drainage. 



Considerable space has been devoted to these 

 untoward results which sometimes follow serum 

 administration, but on the whole they are uncom- 

 mon when reasonably good technique is employed. 

 One who is careful will immunize hundreds and 

 even thousands of hogs without encountering 

 difficulties of this kind, but it is well to know that 

 they sometimes occur, and to understand the im- 

 portance of seemingly trifling influences that 

 operate to cause or prevent them. 



Summary of action of serum alone. 



1. Produces in hogs not infected with cholera 

 near the time of its administration a passive im- 

 munity lasting about four weeks. 



2. Produces active and permanent immunity in 

 swine more than twelve weeks old that are defi- 

 nitely infected with cholera immediately before 

 immunization, or during the three or four weeks 

 following it. 



