440 CONTAGIOUS PLEUROPNEUMONIA IN CATTLE 



is caused by the smallest known bacterium, which was discovered 

 by Nocard and Roux in 1898. The epizootic was first correctly 

 described by Bourgelat in France (1765), but it had previously been 

 noticed in Germany. It has prevailed throughout Europe and was 

 imported to Africa, Asia, and Australia, and introduced into the 

 United States, probably first into New York in 1843. It then spread 

 to various States, but it was vigorously opposed and finally stamped 

 out in 1891, since which time this country has been free from the 

 disease. 



Pathologic Lesions. The principal lesions are generally found 

 only on one side of the thorax and on the pleura of the same side, 

 but there appears to be no predilection as to the side involved. This 

 is true of 75 per cent, of the animals affected. According to Nocard, 

 the pleura is always involved, but in very variable degrees. Sometimes 

 when the inflammatory changes in the lung greatly predominate a 

 certain amount of thickening and infiltration is seen in the pleura 

 pulmonalis of the same side. In a more advanced stage there is 

 vascularization of the serous membrane, with an abundant fibrinous 

 exudate on its surface. The lungs in acute cases are found hepatized 

 in more or less extensive areas; they are void of air and non-elastic. 

 On section a clear, serous, yellowish fluid oozes out of the areas of 

 hepatization. When collected in a clean vessel this fluid subsequently 

 coagulates into a gelatinous mass. The interlobular connective 

 tissue is increased and forms a light yellowish network which divides 

 the hepatized area into irregular patches of various colors. The 

 latter may be gray, light red or dark brown red, so that a cut surface 

 presents a mottled appearance. The increased interalveolar con- 

 nective tissue shows enlarged lymph vessels and clefts filled with a 

 yellowish serous or a more fibrinous exudate. The obliterated 

 alveoli of an area of hepatization are sometimes light red and 

 firm at the periphery, while the centre of the solid tissue has 

 become dark red and soft-elastic. The walls of the bronchi in the 

 affected pulmonary areas are infiltrated, their lumina contain an 

 exudate and the peribronchial and mediastinal glands are quite 

 edematous. While the pleura over the diseased portions of lungs 

 generally shows the changes described above, it may also contain very 

 little fluid between the visceral and the parietal layer or, on the other 

 hand, a large amount of clear yellow fluid or a yellowish-gray cloudy 

 fluid with flocculi of fibrin may be present. When only very small 

 amounts of pleuritic exudate are present the condition is known as 

 pleuritis sicca. On the other hand the amount of fluid may be 15 to 

 20 liters. In some cases the greater portion of the exudate is not 

 found free between the two layers of the pleura, but has infiltrated 

 the mediastinal connective tissue. The latter then forms a soft 

 gelatinous tumor composed of confluent, infiltrated masses of a yellow 

 color. If cut into, these masses discharge an abundant amount of 

 yellowish or decidedly amber-colored serous fluid. . The description 



