382 DISEASES OF CATTLE. 



hand, an area of dullness may be discovered corresponding to the por- 

 tion where the respiratory murmur has disappeared. This loss of res- 

 piration detected by ausculation, and the dullness brought out by 

 percussion, are the most important evidences of an inflamed or consoli- 

 dated lung. 



Seriously affected animals remain standing, if they have sufficient 

 strength, but those which lie down always lie on the affected side. 



The proportion of animals which become affected after being exposed 

 varies according to the virulence of the outbreak, the susceptibility of 

 the animals, and the length of time during which exposure is continued. 

 Sometimes not over 15, 20, or 30 per cent will contract the disease when 

 a large herd is exposed; but, on the other hand, 80 or 90 per cent may 

 be affected. The proportion of cases in which the disease proves fatal 

 also varies greatly it may not exceed 10 per cent and it may reach 50 

 per cent. In general it may be said that about 40 per cent of the 

 exposed animals will contract the disease and about one-half of these 

 cases will prove fatal. 



Post-mortem appear a jwes. Owing to the complexity of the structure 

 of the lung tissue, its ramifications of bronchial tubes and blood-vessels 

 and its abundant supply of lymphatics, the pathological changes in 

 pleuro-pneumonia are but imperfectly understood and interpreted with 

 great difficulty. Our ignorance as to the nature of the exciting cause 

 adds to this difficulty. Furthermore there are certain kinds of pneu- 

 monia which present some resemblances to pleuro-pneumonia and which 

 may therefore be confused with it in some of its phases. 



If we kill an animal affected with acute pleuro-pueumonia and exam- 

 ine the cavity of the chest and lungs the following appearances will be 

 noted: 



The thorax may contain more or less serum, which may be clear or 

 clouded. There may be firm adhesions of different parts of the lungs to 

 the chest wall, the extent of which depends on the stage and severity 

 of the disease. The diseased lobes are unusually large and exceedingly 

 firm to the touch. The weight of a single large lobe may reach 40 

 pounds. Usually only one side is affected, often but a single lobe, and 

 this most commonly the large or principal lobe. The pleura may be 

 covered with one or more layers of a firm, elastic grayish membrane, 

 which varies in thickness and which sometimes may be pulled away 

 entirely. Sometimes it is absent. The pleura, however, is opaque and 

 apparently very much thickened. This is due to the diseased condition 

 of the connective tissue beneath the pleura, as will be explained further 

 on. When ail affected lobe is cut through at right angles to its long 

 diameter the cut surface will present a variety of interesting changes. 

 In the first place, the spaces between the small subdivisions of the lung 

 (the lobules), which in the healthy lung are barely visible, are distended 

 with a yellowish white, usually quite firm, substance, which is coagu- 

 lated fibrin. The cut surface thus appears divided up into small fields 



