Etiology. 135 



the coli group. Poels & Berger described an enzootic pneumonia 

 in calves and young pigs, caused by streptococcus pyogenes. Ba- 

 cillus pyogenes may likewise occasionally produce enzootic bron- 

 chitis and bronchopneumonia in young pigs and calves (Grips, 

 Glage & Nieberle, Olt, Poels, Berger). The bacillus bronchio- 

 litidis vitali described by Kitt is probably identical with the 

 bacillus pyogenes. Poels also ascribes the faculty of producing 

 enzootic pneumonia in young pigs to a staphylococcus pyogenes 

 and to a kind of streptothrix, which he has not described more 

 fully. Finally Berger observed an enzootic pneumonia in 

 calves which was produced by bacillus pyocyaneus. 



The causal relation between enzootic pneumonia and varie- 

 ties of the bacillus bipolaris septicus is now generally considered 

 as being well established. Still, many authors do not believe 

 that the other microorganisms mentioned are at all etiologic 

 factors in the production of enzootic pneumonia and hold that 

 they are present only secondarily, having invaded an already 

 diseased lung. This view appears justilied in those cases in 

 which bacteriologic examinations were made onlj^ in an ad- 

 vanced stage. However, other bacteria than the bacillus bipo- 

 laris have been found in the absence of the latter in very recent 

 cases (Poels, Berger, J. Muller, Kitt, Grips, Glage & Nieberle, 

 Olt) and pneumonia has been produced with them in experi- 

 mental animals by subcutaneous and by intratracheal injection, 

 as for instance by J. Miiller with a bacillus of the coli group and 

 by Junack with a staphylococcus or a streptothrix organism. 



Several kinds of bacteria appear to be effective in some 

 cases. Frequently, however, the presence of bacteria different 

 from the bacillus bipolaris simply represents a secondarj^ infec- 

 tion, particularly when the disease has run a longer course. 

 This furnishes the basis for further tissue changes which may 

 so modify the original pathologic picture that it appears as if 

 we were dealing with a new disease (Holtli). A secondary in- 

 fection of the lungs may occur also in other enzootic diseases 

 (pyosepticemia, dysentery of sucklings, white scours, strangles) 

 and then give rise to numerous cases of bronchopneumonia (sec- 

 ondary bronchopneumonia of sucklings). 



The Etiological Relation Between Enzootic Pneumonia of Young 

 Animals of Various Species. Some incontestable clinical observations 

 furnish the proof that enzootic pneumonia may occasionally be trans- 

 ferred from the young of one species to that of another. Lambs were 

 infected from hogs suffering from swine plague (Keleti, Pr. Vb.). 

 Calves were infected from calves, kids or foals suffering from septic 

 pneumonia (Perroncito, Saner, Pr. A^b., 1905, ii, 17, Bass, Pfeil) ; Riihm 

 & Schreiber likewise consider the spreading of swine plague to calves, as 

 probable or of calf-pneumonia to young pigs. In connection with the pos- 

 itive inoculation experiments mentioned, and the biologic properties of ba- 

 cillus bipolaris, these observations permit the conclusion that the different 

 forms of pneumonia caused by it in calves, pigs, lambs and kids are 

 intimately related or are produced by varieties of the same bacterium. 

 The bacillus bipolaris appears to have adapted itself, in the majority 



