I 78 HOG CHOLERA 



and slightly outside of the ulcer no inflammation of the mem- 

 brane exists. Giant cells have been observ'ed in the intertubular 

 tissues at the edge of the ulcer. The depth to which the infiltra- 

 tion extends is not always limited to the submucosa ; it may 

 extend into the muscular coats and cause inflammatory thick- 

 ening and inflammation and the formation of new vessels in 

 the subjacent serosa. 



In some cases the necrosis, instead of appearing in circum- 

 scribed ulcers from one-sixteenth to one-half inch or more 

 across, involves the whole surface of the mucous membrane, 

 giving it the appearance of a so-called diphtheritic membrane. 

 In such cases the walls of the intestine are very much thick- 

 ened and so friable as to be easily torn wath the forceps in 

 handling them. Such necroses are rare in epizootic cases, but 

 it frequently appears in animals which have been fed with 

 pure cultures of hog cholera bacilli. 



The distribution of the ulcers varies but slightly. They 

 appear most frequently in the caecum and on the ileo-caecal 

 valve, as well as in the upper half of the colon. The lower 

 half is implicated in severe cases only and then less ex- 

 tensiveh-. The rectum is rarely ulcerated. The lower por- 

 tion of the ileum is ulcerated in a small percentage of animals, 

 especially when they have been fed with hog cholera vis- 

 cera or cultures. The stomach is occasionally the seat of 

 slight ulceration. The lymphatic glands of the affected 

 intestine are usually much enlarged, pale, tough and whitish 

 on section. The spleen is rarely enlarged ; the liver shows 

 degenerative changes. The heart and lungs are usually normal. 

 The broncho-pneumonia frequently found in young pigs in the 

 winter months must be ascribed primarily to exposure rather 

 than to the presence of hog cholera. 



In some outbreaks the acute and the chronic types of the 

 disease are not so clearly separated as given in the foregoing 

 pages. Frequentlj^ recent hemorrhagic lesions seem to be 

 associated with cases presenting extensive ulcerations, which 

 certainly are much older than the extravasations. It may be 

 that the latter are the result of a secondary invasion of the 

 hog-cholera virus, either from the ulcers in the intestine or 



