50 The Lung Plague of Cattle. 



blood-stained, when the whole presents a uniform dark 

 mass. This forin has the granular appearance of that lasi 

 described and on microscopic examination its minute 

 blood-vessels are found distended to their utmost capacity 

 with accumulated blood globules. This black consolidation 

 is always sharply limited by the borders of certain lob 

 ules or groups of lobules which are connected with a 

 particular air tube and its accompanying blood vessels, 

 and the artery leading to such lobules is as constantly 

 blocked by a firm blood-clot. The mode of causation is this : 

 The artery being in the centre of a diseased mass, be- 

 comes itself inflamed. As soon as the inflammation 

 reaches its inner coat the contained blood coagulates ; 

 the vein is usually blocked in the same way. The blood 

 formerly supplied by the artery to certain lobules is now 

 arrested ; that in the capillary vessels of these lobules 

 stagnates ; nutrition of the walls of the capillaries ceases 

 and these losing their natural powers of selection allow 

 the liquid parts to pass freely out of the vessels, leaving 

 the globules only in their interior. More blood continues to 

 enter them slowly from adjacent capillaries supplied from 

 other sources, and as this is filtered in the same way by 

 the walls of the vessels, these soon come to be filled to 

 repletion by the globules only, and hence the intensely 

 dark color assumed. The color is often heightened by 

 the escape of blood from the now friable vessels into the 

 surrounding tissue, and it is by this means that the in- 

 terlobular tissue is usually stained. (See Heliotype.) 

 This black hepatization, or as it is technically called, 

 infarction, is an almost constant occurrence in the dis- 

 ease as seen in New York, and the death and en- 

 cvsting of large portions of lung is therefore the rule. 

 If too extensive, of course the patient perishes, but not 

 unfrequently a mass of lung measuring four or six inches 

 by twelve is thus separated without killing the animal 



