104 Croupous Pneumonia. 



fluences act l)y lowering the resistance, to the influenza micro- 

 organism, of the organism as a whole, or of the lungs in partic- 

 ular. It cannot, however, be denied that these external influ- 

 ences play a decided role which may he of sucli importance 

 that the disease would never have occurred without them. These 

 external causes may, in infected stables, lead to a so-called 

 croupous pneumonia, while they will simply produce a catarrhal 

 or interstitial pneumonia in non-infected stables, either after 

 such external influences or without them ; then there still exists 

 the possibility that the influenza virus may have lived in the 

 affected horse as a saprophyte and did not produce any noxious 

 effect in the absence of a harmful predisposing factor. 



Experimenters have not been a])le to produce croupous pneumonia 

 in domestic animals. Diirck, who succeeded a few times in producing 

 croupous pneumonia in small laboratory animals by consideral)le ex- 

 posure to cold, found in all cases bacteria as the direct producers of the 

 inflammatory process. 



Secondary pneumonia is probably likewise due to the 

 influenza bacillus and is sometimes seen after catarrhal influenza, 

 epizootic laryngotracheal catarrh, strangles, hemorrhagic sep- 

 ticemia and purpura hemorrhagica. It does, however, usually 

 not show the course of a typical pneumonia. 



The occurrence of croupous pneumonia independently of 

 pleuropneumonia in cattle is established beyond doubt; it 

 develops usually after the invasion of bacillus bovisepticus 

 (see Vol. I). It is also commonly observed as a foreign body 

 pneumonia after the entrance of foreign bodies from the air 

 passages or from the forestomachs, although it does not show 

 a typical course in these cases and usually takes the course of 

 a catarrhal pneumonia. 



The ol)servation of Jensen, Bucli and Krliger have shown beyond a 

 doul)t that hemorrhagic septicemia of cattle also occurs sporadically. 

 Schiitz found "ovoid" bacteria in the affected lungs in croupous pneu- 

 monia of cattle. Kriiger demonstrated the presence of bipolar bacteria 

 by inoculation experiments. Coulon and Olivier saw croupous pneu- 

 monia in cattle in wet valleys ; Cagny in steers which were kept in the 

 open during cold weather. These affections, however, could not be 

 transmitted by application of the expressed lung juice to the skin de- 

 nuded of its epithelium, or by subcutaneous application with a vaccina- 

 tion lancet. Nevertheless, the negative result does not exclude the possi- 

 bility of pneumonia being caused by the bipolar bacterium, because 

 subcutaneous inoculation is not always successful even when lymph of 

 animals is used which undoubtedly suffer from the pectoral form of 

 hemorrhagic septicemia. 



Hogs suffer from the pneumonic form of swine-jDlague which 

 often assumes a croupous character (see Vol. I). The eases 

 of pneumonia observed by Bayer in Hungary probably belong 

 to this type. Hemorrhagic septicemia whicli sojnetimes spreads 

 from cattle to hogs may likewise form the basis of a croupous 



