INFECTIOUS DISEASES OF CATTLE. 387 



cyst, or capsule around it, gradually collapse and form a cicatrix. 

 This favorable termination takes place t)nly when the dead mass is not 

 too large. It may, however, involve over a half .of one of the large 

 lobes. Under such circumstances recovery is improbable. A more 

 favorable termination is the abundant growth of fibrous tissue around 

 and into the hepatized masses. The formation of fibrous tissue may 

 extend to the pleura, or lung covering, and cause firm adhesion of the 

 lungs to the chest wall and to the pericardium, or heart case. 



The same peculiar inflammatory changes which take place between 

 the lobules of the lung and around the bronchi and vessels may invade 

 the pleural cavity, cause extensive membranous and spongy deposits 

 on the pleura and firm deposits around the heart and large arteries, 

 the gullet, and windpipe. 



These are the main features of the lung disease caused by contagious 

 pleuropneumonia. In the typical acute cases there are a sufficient 

 number of peculiarities to enable us to make a positive diagnosis. 

 There are, however, many cases in which the disease is restricted to 

 small areas, or to the interlobular tissue, or in which the changes are 

 as yet imperfectly developed, or else so far advanced that doubts may 

 arise as to the true nature of the affection. In such cases all obtain- 

 able facts, including the history of the case, the symptoms during life, 

 and the pathological changes observed on post-mortem examination 

 must be taken into consideration. Only one who has made a careful 

 study of the disease is fitted to decide in such cases. 



Other kinds of lung disease may be confounded Avith pleuropneu- 

 monia because of certain features common to most lung diseases of 

 cattle. The inflammation of the connective tissue between the lob- 

 ules is not infrequently observed in so-called interstitial pneumonia 

 and may lead to the fonnation of whitish bands intei-secting the lung 

 tissue in various directions. On the cut surface these bands may give 

 rise to a decidedly marbled appearrnce. Again, in traumatic pneu- 

 monia, due, as its name implies, to the entrance of foreign bodies into 

 the lung tissue, generally fi-om the paunch, the connective tissue 

 around the place of disease becomes inflamed and thickened, and the 

 disease itself may simulate pleuropneumonia in its retrogressive 

 stages when it is confined to a small portion of lung tissue. The 

 filling up of the interlobular spaces with fibrin and connective tissue 

 of inflammatory origin is not thus limited to pleuropneumonia, but 

 may appear in a marked degree in other lung diseases. It must not 

 be inferred from this statement that these interlobular changes are 

 necessarily the same as those in pleuropneumonia, although they may 

 appear the same to the naked eye. We simply note their presence 

 without discussing their nature. 



In general, the distinction l^etween pleuropneumonia and broncho- 

 pneumonia is not difficult to make. In the latter disease the pneu- 



