334 ACUTE GENERAL INFECTIOUS DISEASES 



repeated passing through cattle, although passage through 

 sheep and goats is said to weaken it. 



Natural Infection. — Takes place by direct contact with 

 infected animals or indirectly through hides, meat or dis- 

 eased secretions and excretions, attendants, clothing, food, 

 water, and stable utensils. The disease is readily spread 

 along avenues of transportation by animals which have it in 

 a mild form. The mode of infection is usually through the 

 digestive tract. Transmission through the air does not seem, 

 probable, as inclosing an infected patient by a fence, ditch or 

 even a tight stall partition suffices to prevent the further 

 spread of the disease. One attack generally lends immunity 

 for an indefinite period. 



Necropsy. — The postmortem changes vary somewhat with 

 the severity and duration of the attack. Most conspicuous 

 are the lesions in the mucous membranes which are swollen, 

 reddened, show petechise, croupous, and diphtheritic areas. 

 The cadaver is usually much emaciated and commonly an 

 accumulation of a mucopurulent, yellow or discolored dis- 

 charge is found at the natural openings. The mucous mem- 

 brane of the mouth and pharynx shows petechise, croupous 

 deposits and ulcers, most pronounced in the inner surface of 

 the lips, under the tongue, along the gums and cheeks. While 

 the rumen, reticulum, and omasum present no characteristic 

 changes, the mucosa of the abomasum is swollen, highly 

 reddened, and covered with a viscid, dark-colored exudate. 

 In some cases erosions appear. In the duodenum and ileum, 

 Peyer's plaques and the solitary follicles are swollen, dark red 

 in color, and infiltrated with purulent exudate. The changes 

 noted in the large intestine are similar though usually less 

 marked. The intestinal contents are soft and of a reddish- 

 brown color. The spleen is rarely enlarged; it is usually 

 anemic and smaller than normal. The liver is very light 

 colored, anemic, and very friable. The gall-bladder is greatly 

 distended with a light green, watery or dark-colored bile. 

 The respiratory tract shows catarrhal rhinitis with edema of 

 the submucosa; ulcerous erosions and croupous pseudomem- 

 branes are common. The lungs are edematous, sometimes 

 contain catarrhal pneumonic foci, and frequently interstitial 



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