INFECTIOUS DISEASES OF CATTLE. 383 



by yellowish white bands of varying thickness running in various direc- 

 tions through the lung tissue and beneath the pleura. (Plate xxxii.) 

 These bands may appear honeycombed and the spaces filled with yel- 

 lowish fluid (seruin) or they may be uniformly solid. It \\ill also be 

 noticed that the space immediately outside of and around the artery, 

 vein, and air-tube is similarly broadened by fibrinous deposits. Some 

 authorities look upon these bands as constituting the so-called marbling 

 of pleuro-pneumonia. 



In addition to these changes which have taken place in the connective 

 tissue between the lobules, the lung tissue itself may be markedly 

 altered. Certain areas of the cut surface may be very firm in texture 

 and brownish red in color. The cut surface is granular or roughened, 

 not smooth to the eye. Other areas equally firm may be more grayish 

 yellow in color, still others may be blackish. (Plate xxxui.) Besides 

 these areas which represent solidified (hepatized) lung tissue there may 

 be others which approach the normal lung tissue in color and which are 

 soft and float in water. From these a milky purulent fluid may often 

 be expressed. These different shades are represented in Plate xxxn, 

 Fig. 2 ? within a small compass. Some authorities are inclined to con- 

 sider these variations in color on the same cut surAice as the so-called 

 marbling^of pleuro-pneumonia. It matters not whether we regard the 

 bauds between the lobules or the varying shades of the lobules them- 

 selves as the marbling, provided either or both are peculiar to conta- 

 gious pleuro-pneumouia. If we examine the blood-vessels appearing 

 on such a cut surface they will usually be found plugged within the 

 firmly hepatized regions. The artery contains a dark, soft, removable 

 clot, the vein a grayish pink, granular, fragile plug (thrombus) which 

 adheres firmly to the wall of the vein, and if this be slit open, indica- 

 tions of a diseased condition of the inner coat will be readily detected. 

 When large regions of the lung tissue are hepatized the main air-tube 

 and its branches are usually filled with grayish, cylindrical branched 

 masses of fibrin easily removed, as they do not adhere to the mucous 

 membrane. 



The views of pathologist** differ as to the nature of the earliest 

 changes in plenro-pneumouia, and it is not within the scope of this 

 work to present imperfectly developed or controverted theories. In the 

 foregoing description we have taken as a type the acute pleuro-pueu- 

 monia in its fully developed phase, which can scarcely be mistaken for 

 any other disease. We have seen that there is an inflammatory condi 

 tion of the connective tissue between the lobules, resulting in the exu- 

 dation of coagulahlc lymph. This inflammation is equally marked 

 around the blood vessels and air tubes. It leads to iniiammatory 

 changes in the inner wall of the veins, and these cause the dejiosition 

 of thrombi or plugs in the vessels, which prevent the return of the 

 blood. The blood pumped into the lung tissue through the artery, but 

 unable to get out by way of the vein, leaves the mesh work of capil- 



