Natural Infection. Pathogenesis. X2l 



these parasites may independently cause a severe infection and on the other hand 

 that they may be found in apparently healthy animals, their relation to the etiology 

 of this disease is dimiinished by the fact that not infrequently hemorrhagic septicemia 

 of sheep is present even when such parasites are not found in the animal. (Miessner 

 & Schern do not even mention the presence of parasites in their anatomical findings. 

 Lambs only a few months old may become aflEected with the disease, and the dis- 

 ease may be produced by inoculation of pure cultures.) 



Pathogenesis. After a severe infection the bipolar bacilli 

 multiply very rapidly in the body and produce death in a short 

 time by hemorrhagic septicemia. If on the other hand the infec- 

 tion was less severe or the resistance of the animal relatively 

 .higher, the action of the bacilli would be manifested only in a 

 chronic intoxication which would result in progressive emacia- 

 tion and anemia. In these more frequent forms the debility of 

 the animals favors the entrance of other bacteria (especially 

 streptococci) from the intestinal canal and the air passages into 

 the tissues and body fluids. As a result of this secondary infec- 

 tionchanges develop in the internal organs and the bipolar bacilli 

 in the meantime may have entirely disappeared from the blood. 

 The relatively frequent broncho-pneumonia as well as the less 

 frequent arthritis and tendonitis are as a rule the results of 

 such secondary infections, while the pleuro-pneumonia may be 

 produced independently by the bipolar bacilli. 



Anatomical Changes. In the peracute cases the autopsy 

 reveals the typical findings of a hemorrhagic septicemia (see 

 page 83). 



In the acute form the subcutaneous connective tissue of the 

 anterior portion of the body sometimes shows a gelatinous 

 hemorrhagic infiltration. The mucous membranes of the head, 

 the air passages and of the intestines also those of the aboma- 

 sum are usually inflamed, reddened and swollen, the lymph 

 glands are enlarged, their cut surface is moist and in parts 

 shows diffuse reddening. Frequently there are small hemor- 

 rhages in the serous membranes, in the kidneys and in the lymph 

 glands. In some cases the lungs contain even in this stage dark 

 brownish-red broncho-pneumonic foci, besides serous infiltra- 

 tion of the intralobular connective tissue. The spleen has 

 usually a normal appearance. 



In the subacute form lesions of broncho-pneumonia in the 

 anterior and inferior portions of the lung are almost invariably 

 present. In such cases the pleura, sometimes also the peri- 

 cardium, is frequently covered with fibrinous pseudo-mem- 

 branes, and the serous cavities contain smaller or larger quan- 

 tities of a yellow clear or cloudy fluid. The mucous membrane 

 of the bronchi is usually inflamed, reddened and swollen, while 

 that of the intestines is affected less frequently; in some cases 

 the nasal mucous membrane also shows yellow mucous or 

 fibrinous deposits. The lymph glands of the thoracic cavity 

 are moderately swollen. 



In the chronic cases larger areas of the lungs usually show 



