156 HOG CHOLERA 



and trying to smother the action of virus by large 

 and repeated doses of serum alone previous to 

 simultaneous treatment. In no case have we ob- 

 tained evidence to justify even a suspicion that 

 follow-up treatment does not produce permanent 

 immunity, and we know of no experimental work 

 that contradicts these results. 



The factor of greater safety cannot well be 

 questioned, although it is seldom that hogs with 

 average resistance require follow-up treatment. 

 Simultaneous immunization produces the same re- 

 sult, and is cheaper. But if exceedingly valuable 

 animals are to be immunized, one cannot go amiss 

 in giving a dose of serum alone and following it 

 in a week or two with simultaneous treatment. If 

 the first dose of serum is in the system, already 

 absorbed, when the second dose is given with 

 virus, there can be no question that the hazards 

 are reduced. Exact comparisons of the safety of 

 simultaneous and follow-up treatment are difficult 

 to make, because under ordinary conditions both 

 are nearly 100 per cent effective. We have seen 

 follow-up treatment used in immunizing cattle 

 against rinderpest with losses running less than 

 5 per cent when simultaneous treatment with the 

 same serum and virus caused such heavy losses as 

 to forbid its use altogether. We do not care to 

 generalize too far on this point, but the princi- 

 ples employed in preparing and using the two se- 



