INFECTIOUS DISEASES OP CATTLE. 385 



may simulate pleuro-pneumonia in its retrogressive stages when it is 

 confined to a small portion of lung tissue. The filling up of the inter- 

 lobular spaces with fibrin and connective tissue of inflammatory origin 

 is not thus limited to pleuro-pneumonia, but may appear in a marked 

 degree in other lung diseases. It must not be inferred from this state- 

 ment that these interlobular changes are necessarily the same as those 

 in pleuro-pneumonia, although they may appear the same to the naked 

 eye. We simply note their presence without discussing their nature. 



In general the distinction between pleuro-pneumonia and broncho- 

 pneumonia is not difficult to make. In the latter disease the pneumo- 

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

 Plate xxx. The disease attacks the smaller lobes in their lowest por- 

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

 lung or the back of the animal and 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 contagions pleuro-pneumonia 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 broncho-pneumonia 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 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 intermediate 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 ftbrinous casts of acute pleuro- 

 pneumonia. The iuterlobular tissue may or may not be affected. It 

 sometimes contains loose tibrinous 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 

 intcrlobular deposits and the well-marked pleuritis in pletiro pneumo- 

 nia, there is little chance for confusion between well-developed cases of 

 the*e two lung diseases. 



It should not be forjrottcn, 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 IMS 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 appearance. 

 In the same way broncho-pneumonia may vary as to the parts of the 

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