Natural Infection. j^20 



nieres, Uhlenliuth and Gniichtel proved tlie predisposing influ- 

 ence of colds by experiment, while Salmon and Eatz established 

 the fact that the infection is facilitated by the presence of 

 parasites in the intestinal canal and in the air passages (Ascaris 

 lumbricoides, Echinorhynchus gigas, Strongylus paradoxus). 

 In the presence of such parasites the bacteria may more readily 

 penetrate the affected or injured mucous membrane. There 

 may be also other influences, such as poor condition, exhaustion 

 during transportation, etc., especially in young animals increas- 

 ing the susceptibility to the pathogenic action of these ubiqui- 

 tous organisms, which is usually not- marked. The most impor- 

 tant part, however, in the infection witli the swine plague 

 organisms may be attributed to the virus of hog cholera and the 

 primary infection caused by it, and as a matter of fact in hog 

 cholera outbreaks there are very frequently found changes of 

 organs which are analogous to the swine plague infection (see 

 hog cholera). 



Ovoid bacteria which closely correspond morphologically and in 

 their cultural characteristics with the swine plague organisms were 

 first found in healthy animals by Smith then by Moore, Bang, Jensen, 

 Karlinski, Kitt, Klein and Haiishalter. Sometimes they were only 

 slightly virulent, or not at all. In Jensen's experiments, however, 

 various strains killed mice promptly and Bauermeister found that 

 bacteria which he grew from acinous glands were very pathogenic 

 for test animals, while, on the other hand, Karlinski as well as Beck 

 & Koske succeeded in markedly increasing the virulence of the originally 

 slightly virulent strains. 



While the first appearance of swine plague in healthy herds 

 may be associated with soil infection, and also frequently with 

 weakening influences acting upon the animals, the occasional 

 direct or indirect infection from the first affected animals, like 

 in the other diseases of the hemorrhagic septicemia group, 

 cannot be left out of consideration. Affected hogs pass with 

 their excretions, and especially with the mucus which they 

 cough up, great numbers of very virulent bacilli v/hich then 

 enter the bodies of healthy hogs and may by their great numbers 

 and high virulence produce inflammatory processes in them. In 

 this manner an infected aninial which has been purchased and 

 added to a healthy herd may produce the disease among the 

 other animals. As a matter of fact, however, healthy hogs resist 

 such an infection in most instances. The fact that local out- 

 breaks usually die out rapidly, even without any particular 

 measures of eradication may be attributed to a rapid diminu- 

 tion of the virulence of the infective agent outside of the ani- 

 , mal body. 



As the ovoid bacteria occur also in animals affected with 

 other diseases, or may subsequently enter such affected bodies, 

 they may exert a specific pathogenic action in already affected 

 organs. In this manner a preexisting catarrhal pneumonia may 



