MORBID ANATOMY 57 



ventral lobes may have been derived from the overdistended 

 alveoli, or else a broncho-pneumonia, may have preceded the 

 swine-plague pneumonia. 



In microscopic sections of diseased lung tissue the alveoli 

 and smallest air tubes are found distended with cell masses 

 consisting chiefly of leucocytes. Usually there is very little 

 fibrin and ver}' few red corpuscles in the alveoli, even in cases 

 in which the disease was quite recent. It may be that the 

 stage represented in ordinary croupous pneumonia by the pres- 

 ence of fibrin in connection with the cellular elements is very 

 brief, and that it is speedily replaced by large numbers of leu- 

 cocytes. The large predominence of these elements in some 

 portions of the lungs, as well as beginning fatty degeneration, 

 is probably the cause of the regular mottling of the lungs, as 

 seen from the surface. The little yellowish hazy dots represent 

 alveoli surrounded by the hyperaemic walls. 



The necrotic and caseous changes so frequent in swine 

 plague are most interesting. The latter are usually quite small 

 and disseminated in large numbers over the diseased lobes. 

 The former represent larger masses from a marble to a horse- 

 chestnut in size. They represent tissue which has been des- 

 troyed by the rapid multiplication of swine-plague bacteria in 

 particular localities. Hence the}- are found in all stages of the 

 pneumonia. The large caseous masses may be considered as 

 the result of a slow death of larger areas of lung tissue, due 

 primaril}' to the gradual overdistention of the tissue by leuco- 

 cytes, and hence the gradual cutting off of the blood supply. 

 One is a rapid death due -directh- to highly virulent bacteria, 

 the other a slow death, or a kind of dry suppuration in the 

 later stages of the pneumonia, characteristic of the pig, and 

 due indirectly to the irritation of perhaps more attenuated 

 races of bacteria. In some cases there are extensive hemor- 

 rhages in the interlobular connective tissue. (Fig. 9.) 



The inflammation of the pleura frequently extends to the 

 pericardium. This membrane is opaque, thickened, and its 

 vessels distended. It may be glued to the contiguous lobes of 

 the lungs and covered by a false membrane, smooth or rough- 

 ened, which extend upon the large vessels emerging at its base. 



