54 SWINE PLAGUE 
scattered centers of hepatization (embolic pneumonia). If it enters 
by way of the pleura, the virus will creep along the interlobular and 
peribronchial tissue before it invades the parenchyma, proper. 
In natural infection of swine plague, bacteria seem to enter the 
lung tissue chiefly by way of the air passages. At the same time it 
is not improbable that occasionally they may enter the serous cavities 
first, 7. e., invade the pleural cavities and thence the lungs. This 
probability is shown by inoculation in which intravenous injections 
produced exudative pleuritis and pneumonia of the most dependent 
portions of the lungs covered by the pleural exudate. It is not 
improbable that even in the natural disease the bacteria which have 
gained access to a portion of the lung tissue by way of the air tubes 
reach the pleura covering this portion, and may then by this route 
invade other portions of the lungs. It may be that in this way a 
pneumonia originally single may become double. It has been 
observed that the first pneumonic infiltration of the principal lobe was 
at the point of contact with the diseased ventra! lobe, and that the 
resting of a lobe against an inflamed serous surface, such as the peri- 
cardium, caused a pneumonic infiltration at the point of contact. 
The character and seat of the lung lesions are somewhat variable. 
It is difficult to find two lungs exactly alike so far as gross appearances 
go. This to be sure may be due largely to the fact that animals die 
in different stages of the disease. ‘Yet there are differences evidently 
not dependent on this fact, which must be left for special pathological 
investigation. 
In general the cephalic (anterior) half of a swine-plague lung is 
hepatized, of a dark-red or grayish-red color and firm to the touch. 
The pleura is more or less thickened and opaque, and possibly covered 
with easily removable, friable, false membranes. In the more 
recently affected regions a faint but quite regular, delicate mottling 
with yellow is observed to shine through the pleura when not thick- 
ened. These minute hazy, yellowish dots usually occur in groups of 
four. Occasionally whitish or yellowish patches varying much in 
size are seen, perhaps more frequently in the ventral lobes. These 
correspond to homogeneous dead masses of lung tissue. 
When such lungs are cut open, the section presents much the same 
appearance, both as regards color and mottling, as when viewed from 
the surface, excepting that the details are less distinct. In some 
cases, in the most recently invaded areas in the principal lobe and 
nearer the dorsum in the other lobes, the dark or grayish-red cut 
