EEPOET OF THE BUREAU OF ANIMAL INDUSTRY. 109 



animal) and in the expanded state covering the heart laterally, the other extending 

 towards the head and overlapping the base of the heart. These small lobes may be 

 denominated the ventral and cephalic lobes, respectively. The right cephalic lobe 

 is longer and more distinct from the ventral lobe than the corresponding left ce- 

 phalic. Wedged in between the two principal lobes and resting on the diaphragm 

 is a small lobe, pyramidal, belonging to the right lung (azygos lobe). This lobe 

 rests on the left against the mediastinal membrane, and on the right it is separated 

 from the right principal lobe by a fold of the pleura passing from the ventral ab- 

 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. Very- 

 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 gees 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 centimeters 

 from the bifurcation the trachea gives off a small bronchus, which supplies the right 

 cephalic 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 clew 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 then enters the air tube of the small median lobe, and then 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. It is a 

 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- 

 kation between the diseased and healthy lung tissue is nearly hori- 

 zontal, 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 cephalic, 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, i. e. , on either side of the verte- 

 bral column, was involved. When the disease progresses it is upward, 

 i. e. , towards the back-bone of the animal, invading the still spongy 

 tissue by lobules and groups of lobules. 



If "we put tft^ether the^ facts brought out hi the preceding pages 

 we can construct a theory as to the manner in which the virus enters 



