388 DISEASES OF CATTLE. 



monia generally invades certain lobes, as indicated by the dotted line 

 on Plate XXX. The disease attacks the smaller lobes in their lowest 

 portions first and gradually extends upward, i. e., toward the root of 

 the lung or the back of the animal and backward into the large prin- 

 cipal lobes. Again, both lungs in advanced cases are often symmetri- 

 cally affected, as shown b}' the dotted line on both lungs in the plate 

 referred to. In contagious pleuropneumonia the large principal lobe 

 of one side is most frequently affected, and a symmetrical disease of 

 both lungs is very rare, if, in fact, it has ever been observed. The 

 lung tissue in bronchopneumonia is not enlarged, but rather more 

 contracted than the normal tissue around it. This is well illustrated 

 in Plate XXXI. Normal air-containing lobules may be scattered 

 among and around the hepatized portion in an ii-regidar manner. In 

 pleuropneumonia the diseased and healthy portions are either sharply 

 divided off, one from the other, or else they shade into each other 

 by intermediate stages. 



The hei^atized lung tissue in bronchopneumonia Avhen the cut sur- 

 face is examined is usuall}'' of a more or less dark flesh color with paler 

 grayish yellow dots regidarly interspersed, giving it a peculiar mot- 

 tled appearance. In the more advanced stages it becomes more firm, 

 and may contain nodular and firmer masses disseminated through it. 

 The air tubes usually contain more or less soft creamy or cheesy pus 

 or a turbid fluid quite different from the loose fibrinous casts of 

 acute pleuropneumonia. The interlobular tissue may or may not be 

 affected. It sometimes contains loose fibrinous plugs, or it may be 

 gi-eatly distended with air, especially in the still noiTnal portions of 

 the lung. The pleura is seldom seriously diseased. If we contrast 

 with these features the firm dark-red hepatizations, the plugging of 

 the veins, the extensive interlobular deposits, and the well-marked 

 pleuritis in pleuropneumonia, there is little chance for confusion 

 between well-developed cases of these two lung diseases. 



It should not be forgotten, however, that the lesions of the disease 

 known as contagious pleuropneumonia may be confined to the serous 

 membranes of the thorax, or they may be confined to the parenchyma 

 of the lungs; they may affect a whole lobe, or only a small portion of 

 the lobe; they may or may not cause the so-called marbled appear- 

 ance. In the same way bronchopneumonia may vary as to the parts 

 of the lung affected, the extent of the lesions, the degree and kind of 

 pathological changes in the interlobular tissue, the color of the lung 

 on cross section, and the amount of hepatization. In individual caseSj 

 therefore, it is often necessary to take into account the history of the 

 animal, the course of the disease, and the communicability of the 

 affection before a diagnosis can be made between the two diseases. 



Prevention and treatment. — The prevention of pleuropneumonia, as 

 of other contagious diseases, consists in keeping animals so that they 



