INFECTIOUS DISEASES OF CATTLE. 373 



nia generally invades certain lobes as indicated by the dotted line on 

 PI. XXX. The disease attacks the smaller lobes in their lowest por- 

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

 lung or the back of the animaland backward into the large principal 

 lobes. Again both lungs, in advanced cases, are often symmetrically 

 affected, as shown by the dotted line on both lungs in the plate referred 

 to. In contagious pleuro-pneumonia the large principal lobe of one 

 side is mpst frequently affected, and a symmetrical disease of both 

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

 tissue in broncho-pneumonia is not enlarged, but rather more con- 

 tracted 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 irregular manner. In pleuro- 

 pneumonia the diseased and healthy portions are either sharply divided 

 off, one from the other, or else they shade into each other by interme- 

 diate stages. 



The hepatized lung tissue in broncho-pneumonia when the cut sur- 

 face is examined is usually of a more or less dark flesh color with paler- 

 grayish yellow dots regularly interspersed, giving it a peculiar mottled 

 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 

 pleuro-pneumonia. The interlobular tissue may or may not be 

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

 greatly distended with air, especially in the still normal 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 pleuro-pneumonia, 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 pleuro-pneumonia 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 broncho-pneumonia 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 cases, 

 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 pleuro-pneumonia, as 

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

 will not be exposed to the contagion. As the disease only arises by 



