78 



SWINE PLAGUE 



usually the ventral lobes are first attacked, then the cephalic 

 and azygos, and lastly the principal lobes. This movement of 

 the disease seems to depend on gravity, inasmuch as the dis- 

 eased parts are marked off from the healthy portion by a nearly 



horizontal line. I n 

 other words, the most 

 dependent portions of 

 the lungs are the ones 

 affected first, and as 

 the disease progresses 

 upwards only a small 

 portion of the princi- 

 pal lobe directly un- 

 der the back of the 

 animal remains per- 

 vious, provided the 

 life of the animal is 

 maintained up to this 

 poi nt . In cases where 

 disease is caused by 

 lung worms or by em- 

 bolism, the pneu-- 

 monia involves por- 

 tions of the principal lobes not contiguous to the ventral lobes. 

 Two kinds of pneumonia are encountered, namely, lobar 

 and catarrhal or broncho-pneumonia. In the former the vesi- 

 cular portion of the lung substance is chiefly affected ; in the 

 latter the smaller bronchioles are primarily attacked and the 

 alveoli secondarily. In croupous-pneumonia, there is, follow- 

 ing the stage of congestion, an emigration of red blood cor- 

 puscles, some leucocytes, and an exudate of fibrin into the air 

 spaces. These elements are firmly matted together by the 

 coagulating fibrin, making the diseased lung firm to the touch. 

 In broncho-pneumonia the catarrhal condition of the smaller 

 air tubes makes them impervious to air. The lung tissue 

 which they supply is gradually emptied of air and assumes the 

 appearance of red flesh, owing to the collapse of the walls of 



Fig. 10. 



Portion of a pig's 

 emphysema. 



lung showing 



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