MORBID ANATOMY 



55 



the virus will creep along the interlobular and peribronchial 

 tissue before it invades the parenchyma proper. 



P'iG. 8. Right lung of pig. The stippled portion is usually involved 

 i7i cases of infectious pneumonia or S7vine plague, {b) cephalic lobe, [c) ven- 

 tral lobe, [a] principal lobe. The ventral lobe is usually the seat of the 

 more advanced disease and consequently the first to becoDie hepatized. The 

 cephalic portion of the principal lobe (.r) is usually hepatized and the 

 remaining portion deeply reddened. 



In natural infection the swine-plague bacteria seem to 

 enter the lung tissue chiefly by way of the air tubes. At the 

 same time it is not improbable that occasionally the}' may 

 enter the serous cavities first, z. e., invade the pleural cavities 

 and thence the lungs. This probability is shown by inocula- 

 tions in which intravenous injections produced exudative pleu- 

 ritis, and pneumonia of the most dependent portions of the 

 lungs covered by the pleural exudate. It is not improbable 

 that even in the natural disease the bacteria which have 

 gained access to a portion of the lung tissue by way of the air 

 tubes reach the pleura covering this portion, and may then b}- 

 this route invade other portions of the lungs. It may be that 

 in this way a pneumonia originally single may become double. 

 It has been observed that the first pneumonic infiltration of 

 the principal lobe was at the points of contact with the dis- 



