388 DISEASES OF CATTLE. 



disease. To these it may be answered that it is the only method -which 

 has ever proved successful, and that in the end it is much more eco- 

 nomical than temporizing measures. 



Inoculation has been adopted in many countries, and has undoubt- 

 edly lessened the death rate, but the disease is kept up and spreads 

 where this practice is allowed. For this reason it should be prohibited 

 wherever there is a possibility and disposition to eradicate the con- 

 tagion. 



PLEURO-PNEUMOXIA. 



[Description of plates.] 



PLATE XXX. The dorsal or upper surface of the lungs of the ox reduced to one 

 sixth of the natural size : a, a', the right and the left principal lobe. Those are the 

 largest and are situated posteriorly, resting upon the diaphragm ; &, I', the ventral 

 lobes, situated between the principal lobes, and c, c', c", the most anterior or 

 cephalic lobes; c, c', c", anterior or cephalic lobes. The right auterior is divided into 

 two lobes (c, c'), the left is single (c") ; d, trachea or windpipe. 



Those portions of the lung tissue lying outside of the dotted lines are the ones 

 most commonly affected in the ordinary types of pneumonia. In the majority of 

 the lungs examined in the laboratory of the Bureau, which were affected with con- 

 tagious pleuro-pneumonia, the principal lobes (a, a') were primarily affected. 



PLATE XXXI. The ventral or middle lobe of the right lung affected with collapse 

 and beginning broncho-pneumonia. The light yellowish portions represent healthy 

 lung tissue, the red represents the disease. It will be noticed that the lines between 

 the lobules are quite faint, indicating little or no inflammation of the connective 

 tissue between the lobules. The healthy lung tissue is seen to be raised above the 

 level of the diseased portion. In contagious pleuro-pneumouia the exact reverse is 

 the case, the diseased portions being very much larger than the healthy. 



PLATE XXXII. Appearance of a cow's lung affected with contagious pleuro-pneu- 

 monia when sections or slices are made of it and cut surfaces examined. Fig. 1. 

 Transverse section through the right principal lobe in a case of acute pleuro-pneu- 

 inonia. The area drawn includes the air -tubes, veins, and arteries, and illustrates 

 the great thickening of the interlobular connective tissue into broad whitish bands, 

 and of the walls of the air-tubes, veins, and arteries: a, air-tube, cut obliquely; a', 

 air-tube cut directly across ; b, arteries cut across ; c, large vein completely occluded 

 by a thrombus, or plug formed during life. The great thickening of the walls of the 

 artery and vein in this disease is especially brought out by stating that in the 

 healthy lung they are so thin as to be easily overlooked. Fig. 2. Transverse sect ion 

 of the principal lobe in a case of acute pleuro-pneumonia, illustrating the different 

 kinds of hepatization or consolidation of the lung. These arc indicated by the 

 different colors from dark red to reddish yellow. This variation of color is regarded 

 by some as the real marbling characteristic of pleuro-pneuuionia, while the whitish 

 bands penetrating the lung tissue in all directions constitute the true marbling ac- 

 cording to other observers. 



PLATE XXXIII. Illustrates what are called infarctions in pleuro-pneumonia. The 

 right half of the figure shows nearly normal lung tissue. The left represents a 

 blackish mass in Avhich the lung tissue is filled with blood and solidified. This is 

 caused by the plugging of the vein carrying away the blood from this portion. 

 The heart forces the blood through the artery into the tissue at considerable pres- 

 sure, but, owing to the fact that its return is prevented, the minute blood-vessels 

 rupture and the air vesicles become distended with blood which coagulates and 

 causes the firmness of the tissue. 



