Nature of the Lung Plague. 53 



tubes, and if it attacks most severely the most delicate 

 and susceptible parts, the membrane lining the smallest 

 branches, it will determine the cloudy swelling so con- 

 stantly seen in these. As the deeper layers and the adja- 

 cent connective tissue is invaded, the exudation and cell 

 proliferation giving rise to the extensive thickening of the 

 peribronchial tissue, as already described, will compress the 

 different vessels and obstruct the flow of liquids through 

 them. The lymphatics as being incomparably the most 

 delicate and compressible will be the first to suffer and 

 the obstruction of these will lead to engorgement and 

 dropsy in the parts from which they draw the lymph. 

 The lymphatic vessels and networks are marvelously 

 abundant in the interlobular tissue and few and small in 

 the lung lobules themselves, hence the obstruction of 

 these vessels as they lead out from a given section of lung 

 will lead to a dropsical effusion into the interlobular tis- 

 sue while the inclosed lobules are still comparatively un- 

 affected. This sufficiently explains the excessive liquid 

 exudation into the interlobular spaces without starting 

 with the assumption that this is the primary step of the 

 disease. 



The subsequent congestion, exudation and cell-prolifera- 

 tion in the lobules themselves sufficiently account for the 

 changes which these subsequently undergo. 



2. If, on the other hand, the infecting material succeeds 

 in reaching the air cells it will, of course, make its earli- 

 est inroads on their delicate walls. Then will follow the 

 early congestion, redness and consolidation of the lobules, 

 and, only later, the extensive interlobular exudation, when 

 the disease in the air tubes and the extensive exudation 

 around them shall have compressed the accompanying 

 lymphatic vessels. In this way is explained the second 

 manner of invasion which I have described above. 



The records of inoculation abundantly suppojt these 

 views. Though a number of experiments record the oc- 



