Pathogenesis 83 



exudates or body fluids under artificial conditions, if li^ht and air are excluded; 

 whereas, in artificial media in the presence of air they are sometimes very rapidly 

 attenuated and finally lose their virulence. 



Pathogenesis. Bipolar bacilli which penetrate into the 

 tissue fluids of the animal organism, produce different patho- 

 logical changes, according to the degree of their virulence and 

 the susceptibility of the animals. In case of a severe infection 

 a peracute hemorrhagic septicemia develops. The bacilli mul- 

 tiply very rapidly and in a short time permeate the entire body, 

 causing death in from 18 to 24 hours. The animals manifest 

 high fever, weakness of the heart, debility, sometimes diarrhea. 

 Autopsy reveals numerous hemorrhages in the tissue of the 

 serous and mucous membranes and parenchymatous organs. 

 The spleen is only slightly swollen, w^hile the Ijanph glands show 

 a marked acute swelling. 



When the infection is somewhat less severe the acute attack 

 lasts for several days when frequently a sero-fibrinous inflam- 

 mation develops on the serous membrane, while the mucous 

 membranes are affected with a hemorrhagic inflammation. With 

 these an inflammation of the joints and tendons is not infre- 

 quently associated. The autopsy reveals in these cases a mod- 

 erate acute swelling of the spleen and a pronounced swelling of 

 the lymph glands in addition to blood extravasations. 



An infection of a milder degree, for instance an intravenous 

 injection of a small quantity or very weak virus, results in 

 some cases in a chronic affection, lasting for several weeks 

 or months. The animals become emaciated slowly but gradu- 

 ally, frequently in spite of their good appetite; they have an 

 intermittent fever, and inflammatory processes develop in dif- 

 ferent joints, especially in the knee, carpal and tarsal joints. 

 The animals also show a marked predisposition for secondary 

 infections, especially for catarrhal pneumonia. 



The bipolar bacillus may produce these varied clinical 

 manifestations independently. In the acute cases the organism 

 is found in great numbers in the blood and also in the exudates 

 in pure culture. The pathological processes in some of the 

 chronic cases may be also attributed to its action even if the 

 bacilli have since disappeared from the body. 



The local action of bipolar bacilli is manifested in the 

 production of serous and fibrinous inflammations, later in 

 degeneration of the exudate and tissue elements, as a result of 

 which dry caseous masses occur, while necrotic areas develop 

 in the affected organs. The necrosis is very probably the result 

 of the action of toxins. Filtrates of bouillon cultures free from 

 bacteria usually produce only a very slight or no toxic action. 

 Killed masses of bacteria, however, possess distinct toxic prop- 

 erties. Inasmuch as in the body of the animal both multipli- 

 cation and destruction of bacilli take place, and as dead bacilli 

 are dissolved in the tissue fluids the toxins which are eliminated 

 may cause general effects and local necrotic processes. There 



