BUREAU OF ANIMAL INDUSTRY. 515 
first, and its extension upwards as it gains upon the vitality of the 
lung tissue, all accord with this theory. At the same time it har- 
monizes with the fact that the microbe causing the disease can not 
survive drying for even a single day. 
In this disease the lungs are primarily the seat of the virus, and in 
them the greatest changes are observable. The lesions are those of 
a broncho-pneumonia. The pleura is secondarily involved over the 
seat of the disease when this extends to the surface of the lungs. 
The great variety in the appearance and extent of the lesions as 
manifested in different cases may be brought together under a few 
heads for description. 
The most severe types of disease are encountered at the beginning 
of an epidemic, and may be conveniently denominated acute. Plates 
I and I] arg illustrations made from the right lung of pig No. 407, 
described in the preceding pages. As may be seen, there is exten- 
sive pleurisy accompanying the pneumonia. The disease is charac- 
terized by a solidification of the ventral, cephalic, and median lobes, 
and a portion of the principal lobe, usually of both lungs. The dis- 
eased lobes are moderately expanded, so that the thorax seems almost 
filled up with lung tissue when the sternum is removed. The hepa- 
tized portion has a bright blood-red color, when viewed from the 
surface, as well as on section. The surface in many cases has a 
peculiar.mottled aspect, shown in Plate III, Fig. 2. The bright-red 
ground is dotted with closely set, grayish-yellow points, arranged 
quite regularly in groups of four, occasionally of three. These points 
are not sharply defined, but hazy. When examined with a: lens this 
haziness is well marked. This grayish mottling does not appear 
everywhere on the diseased lung, but only upon some lobes, and then 
with striking clearness and uniformity. These points no doubt are 
the terminal air sacs, or infundibdula distended with the cellular ex- 
udate. The more leucocytes in the exudate the whiter the injection 
will appear through the translucent: pleura. The occlusion of the 
air cells and bronchi by catarrhal products and the mottling due to 
it may, however, be seen in lungs free from swine plague bacteria 
(simple broncho-pneumonia). The bacteria are found imbedded in 
the cellular masses, which occlude the alveoli. The disease involves 
the terminal air tubes, as they are frequently found packed with 
cells. The larger bronchioles and bronchi are the seat of catarrhal 
changes. The lumen of the tubes is filled with a muco-purulent se- 
cretion, usually containing large numbers of bacteria. 
The foregoing may be regarded as the early stages of the disease 
roper. When the invasion is thus extensive and takes place sud- 
enly, the animal speedily succumbs before the disease has had the 
opportunity of entering upon the more advanced stages. But in per- 
haps the majority of animals the disease progresses very slowly. 
It may be that only the ventral lobes are attacked at first, and then 
only in certain limited areas. The surrounding tissue becomes hyper- 
emic and often consolidated. The areas first attacked become con- 
verted into homogeneous greenish or yellewish-white masses, sharply 
defined from the surrounding tissue. They cut like ordinary hard 
cheese, and on microscopic examination are found to be made up of 
dead lymphoid cells and bacteria of all kinds. The process of casé- 
ation is without doubt caused by the packing of the respiratory tis- 
sue with cells, by which the capillaries are compressed and all food 
supply cut off. The caseous foci vary from the size of a small pea 
to that of a marble or horse-chestnut. (Plate IV, Fig. 1.) They are 
