140 HOG CHOLERA 



is so light that symptoms do not appear, but if 

 temperatures are recorded the curve will usually 

 show slight elevation and more or less fluctuation 

 between the fifth and twelfth days following immu- 

 nization. Under unfavorable conditions the reac- 

 tion becomes relatively more severe, and symp- 

 toms of hog cholera may appear. If these are 

 slight, complete recovery will take place; if they 

 are severe, they threaten the life of the animal; 

 and if it dies its death is due to hog cholera just 

 as truly as it would be if no serum were adminis- 

 tered^. Sickness and deaths due to hog cholera 

 following simultaneous treatment are termed 

 "breaks" or "vaccination cholera." If the trou- 

 ble appears during the first three weeks following 

 treatment it is called a "serum break" the suppo- 

 sition being that the serum is impotent and allows 

 the virus to kill the animal ; if it appears after a 

 longer time it is termed a "virus break, ' ' the effect 

 being ascribed to the fact that inert virus has been 

 administered and the serum produces only a tem- 

 porary immunity, which, as it disappears, leaves 

 the herd again susceptible. 



In reality, ' ' serum breaks ' ' are due to a variety 

 of causes, among which are impotent serum, 

 faulty technique in vaccinating, insufficient doses 

 of serum, and, in addition, any influence whatso- 

 ever that temporarily lowers the resistance of the 

 animals during the two or three weeks subsequent 



