Lung Plague of Cattle. 655 



dimate or hot season, under which large herds may die without a 

 single exception, the disease running a fatal course in two or 

 three days. In cooler climates 20 per cent, will often escape at 

 first (French Commission Experiments, 1849). 



Lesions. If death has taken place early, the lesions are 

 usually essentially pulmonary, though they may implicate the 

 pleurae and mediastinum. In many cases the lung alone is in- 

 volved, yet even then the predilection of the microbe for the 

 lymph' network of the interlobular tissue is strongly manifested 

 in the serous infiltration of that, rather than of the lung structure 

 proper. This determines the much talked of marbled lung, the 

 pulmonary lobules standing out at first as a more or less deep red 

 brown or black, while the marbling is caused by the yellowish or 

 grayish infiltrated tissue surrounding each pulmonary lobulette 

 which appear set in, as in mosaic on the surface of a section. 

 Sometimes a blood extravasation discolors the interlobular exu- 

 date as well, yet it retains its soft liquid appearance which suf- 

 ficiently distinguishes it from the firmer lung tissue. These yel- 

 lowish interlobular markings vary much in thickness, but in 

 acute cases this may be up to half an inch or even more. In the 

 lesions of longer standing the interlobular exudate has usually 

 coagulated, or even undergone fibroid organization, so that it 

 compresses and condenses the lobules which it surrounds! 



The pulmonary lobules may show the earliest changes of the 

 alveolar and lobular capillaries, with formation of an exudate, 

 and an active proliferation of small round cells in and around the 

 alveoli. Later the exudate coagulates, forming the familiar 

 red hepatization, and this in its turn may pass into the gray, or it 

 may liquefy and undergo absorption and resolution. Other 

 changes are not uncommon. The excess of interlobular exudate 

 will compress the pulmonary lobules so as to reduce their size 

 and expel the blood from their structure, giving them a pale 

 color, or this compression becomes still greater, completely ar- 

 resting the circulation and inducing lobular gangrene. Thrombi 

 in. the afferent and efferent vessels contribute to the necrotic 

 change, and sequestra of varying size, from that of a nut to that 

 of an infant's head or larger, are formed. The earliest stage of 

 this necrosis is usually infarction of the lung, a definite area of 

 •which becomes saturated with dark blood cells so that in contrast 



