514 REPORT OF THE. COMMISSIONER OF AGRICULTURE. 
dominal wall to inclose the inferior vena cava. This small lobe is almost completely 
shut off, therefore, from the other lobes by folds of the pleura. 
When the trachea and its branches have been examined it is easier to understand — 
this division into lobes. The trachea divides in the thorax into two principal 
branches or bronchi. These bronchi pass into the principal lobes, straight to the 
caudal border, giving off a number of small branches along their course. Ve 
near the place of bifurcation the left bronchus gives off a large branch, which rami- 
fies in the substance of the left ventral lobe. From this branch another goes to the 
cephalic lobe. In some lungs the branches for these two lobes arise together by a 
very short, scarcely perceptible trunk, and are of nearly equal size. The bronchial 
supply of the right lung differs materially from that of the left. About 3™ from — 
the bifurcation the trachea gives off a small bronchus, which supplies the right ce- 
phalic lobe exclusively. At the bifurcation the right bronchus sends a branch to 
the ventral lobe. A short distance from this the same bronchus sends a short branch 
to the small median or azygos lobe. 
These brief remarks will be sufficient to give a general idea of the 
gross anatomy of the pig’s lung. The manner in which the air tubes 
branch gives us a clue as regards the invasion of. the disease itself. 
The bacterial virus entering the trachea first enters the air tubes 
supplying the ventral and cephalic lobes. These become consolidated. 
It 1A enters the air tube of the small median lobe, and ther it in- 
vades the smaller branches of the principal lobe nearest the trachea. 
This is the farthest point to which we have seen the disease advance 
before the animal succumbed. 
A careful inspection of the autopsy notes will show that this is the 
course of the invasion. No case has yet come to our notice in which 
the ventral lobes were normal, while the principal lobe was in part 
consolidated. In many of the cases the disease was cut short by the 
death of the animal before it had reached the principal lobe. It would 
be interesting to know whether or not the right cephalic lobe, which is — 
the first to receive its bronchus, and moreover directly from the tra- 
chea, is first affected. It is difficult to decide this matter, as the ani- 
mals do not die until the disease has made some headway. Itisa 
matter of common observation that in collapse and catarrhal condi- 
tions the ventral lobes are chiefly involved. But there is another 
peculiar feature which will explain the location of the disease much 
better. When the lungs are taken from the thorax and held in the 
position which they occupy in the standing animal, the line of demar- 
cation between the diseased and healthy lung tissue is nearly hori- 
izontal, all below this being consolidated. If gravity has any influ- 
ence upon the virus in selecting its place of attack, we should expect 
to find the ventral lobes first involved, next the cephale, and lastly 
the ventral portions of the principal lobes and the median lobe. This 
course is nearly the same as that given above when the bronchial sup- 
ply was discussed. We have not yet seen lungs in which the upper- 
most portion of the principal lobes, 2. e., on either side of the verte- 
bral column, was involved. When the disease progresses it is upward, 
4.e., towards the back-bone of the animal, invading the still spongy 
tissue by lobules and groups of lobules. 
If we put together the facts brought out in the preceding pages 
we can construct a theory as to the manner in which the virus énters 
the lungs. The course of the invasion shows that the virus is not 
inhaled with the air, that it is not suspended in the air as a living 
germ, otherwise it would be difficult to explain the peculiar localiza- 
tion and the slowly progressive nature of the disease. A virus im- 
bedded in some liquid vehicle will perhaps explain all the facts most 
satisfactorily. Its slow movement from bronchus to bronchus, its 
limitation by gravity to the most dependent portions of the lungs at 
