214 Manual of Veterinary Microbiology. 



MM. Cornil and Chanteraesse also conclude that the 

 germ may penetrate by the respiratory passages and 

 according to the way by which it is introduced, the 

 disease will act more particularly upon the intestines 

 or upon the lungs. 



According to Salmon, the natural virus is subject to 

 considerable variations of activity, and this explains 

 the sometimes rapid and sometimes slow course of the 

 disease. 



The local lesions which follow its penetration assume 

 the general character of an inflammation with a ten- 

 dency to early mortification ; this tendency is sufli- 

 ciently demonstrated by the diphtheritic exudates and 

 ulcerations of the intestinal mucous membrane and 

 the coagulative necrosis, under the form of caseous 

 masses, in the glands of diseased hogs. This charac- 

 ter also shows itself in the mouse, rabbit, guinea pig 

 and pigeon which have been subjected to exj)erimental 

 inoculation. 



The local alterations lead to emaciation of the af- 

 fected animals, but this enfeeblement is complicated 

 with an intoxication. We have already seen that a 

 toxic ptomaine has been isolated from cultures of 

 pneumo-enteritis, and it may be that this poison, se- 

 creted in greater abundance by very virulent germs, is 

 the cause of the vascular changes met with in acute 

 cases. 



The resistance of the bacteria to desiccation, and 

 the facility with which they multiply in water at the 

 ordinary temperature, are conditions which favor the 

 persistence of the disease in one place and the produc- 

 tion of new centers of infection. 



Attenuation. Vaccination. — Attempts at attenuation 



