PATHOLOGY AND POSTMORTEM DIAGNOSIS 125 



(2) The direct cause is some sort of a virus, which is so very- 

 small that we are unable to find it even with the most perfect 

 microscopes. 



(3) There are a large number of predisposing causes which 

 act as aids to the hog-cholera germ or virus in getting a foothold 

 in a herd, and in spreading it from one herd to another. The 

 most important of these predisposing causes are — 



Age. — Young animals being particularly susceptible. 



Sex. — Male animals being slightly more resistant to cholera 

 than the female. 



Breed. — No breed has a perfect immunity to cholera. Mule- 

 foot hogs regarded as very resistant. Pure breed animals less 

 often attacked than the crossed breeds. Too close inbreeding 

 might also be mentioned as a factor which tends to decrease the 

 disease-resisting powers of the animals and makes them more sus- 

 ceptible to cholera. 



Season. — Cholera being especially a disease of the late summer 

 and early fall months, frosts of winter usually check its spread. 



Geographic Location. — Cholera attacks herds in all parts of 

 the world. Found in all parts of the United States, and appears 

 almost equally severe in all localities. IlHnois, Iowa, Indiana, 

 Ohio, and Missouri are especially the seat of extensive yearly out- 

 breaks of cholera, with consequent enormous losses. 



Pathology and Postmortem Diagnosis of Hog- 

 cholera 



The changes produced in the tissues of the sick hog by the 

 virus of hog-cholera are very widely distributed throughout the 

 body and vary greatly in different cases, but in a general way 

 may be regarded as more or less constant. In some cases there 

 are very marked changes produced in the organs found in the 

 thoracic cavity — that is, in the lungs and heart — while in other 

 cases the changes in these organs are comparatively slight, and 

 are replaced by very extensive lesions in the organs of the ab- 

 dominal cavity. Still other carcasses are found in which there 

 are very marked changes in both the thoracic and abdominal vis- 

 cera. 



