INFECTIOUS DISEASES 303 



vaccinated ag'amst hog cholera, particularly if good sanitation is not 

 observed.. It has been noted many times as being concomitant with 

 necrobacillosis ; in short, the infection being almost universally dis- 

 tributed, may be expected to set up a disturbance in a great variety 

 of conditions where the vitality of the exposed animal is lowered. 



The amount of infection present also has its bearing on the exten- 

 sion of the disease, since once it has become active in any of the indi- 



Infected (inflamed) anterior lobes of lungs 



Fig. 85. Hog lungs with chronic swine plague, anterior lobes affected. 



(Ostertag.) 



viduals of a given herd, swine plague is quite apt to extend to ail 

 swine associated with' the affected animals, even though they may 

 seem healthy and apparently possess a normal resistance to the in- 

 fection, i ' 



Source of infection. — Bacilli suisepticus, like the other represen- 

 tatives of this group, are widely distributed. They are frequently 

 found in the respiratory passages of normal swine. Their virulence 



