22 



respect the walls of the air-sacs ; but as the lobulettes are originally 

 separate and independent bodies, as seen in the foetal lung, it is pro- 

 bable that the vessels of each are distinct. If so, there must be, 

 where the walls of two lobulettes are in contact, two layers of capil- 

 laries lying side by side ; and from the mode of formation of the 

 lobulettes, and from the fact that I have been able, in some prepa- 

 rations of the adult lung, partially to separate the lobulettes from 

 one another, I believe that their vessels are distinct, that they ter- 

 minate in their proper radicle-vein, and that thus the capillaries on 

 the outer wall of the lobulette are only exposed on one side to the 

 atmosphere. 



The Bronchial Vessels. It has long been held that the bronchial 

 arteries are distributed to the air-tubes, the areolar tissue, and the 

 vessels of the lungs, and that they pour their contents partly into 

 the pulmonary veins, and partly into certain deep bronchial veins, 

 which have been described by most anatomists as accompanying the 

 arteries within the lungs. An opinion has also been entertained 

 that a communication exists between the bronchial vessels and the 

 branches of the pulmonary arteries. Without referring to the ex- 

 periments and results of other observers, I proceed to state my own. 



My observations have been made on the lungs of the cat, the dog, 

 the rabbit, the pig, the calf, and the sheep, as well as on those of 

 man. The following remarks have special reference to the results 

 obtained in the human lung. 



When the pulmonary artery is injected so that the fluid reaches 

 the pulmonary plexus but does not pass to any extent into the pul- 

 monary veins, the blood-vessels of the bronchial mucous membrane 

 and of the other portions of the bronchial tubes never become in- 

 jected. When, however, the injection is continued so as to fill the 

 pulmonary veins, the vessels of the bronchial tubes become partially 

 injected. 



When the pulmonary veins are injected, whether the pulmonary 

 plexus be well-filled or not, the vessels of the bronchial tubes and of 

 the bronchial mucous membrane are always injected. The bronchial 

 tubes are often seen to be injected when the pulmonary plexus is 

 only very partially so, the fluid seeming to find its way from the 

 pulmonary veins into the vessels of the bronchial tubes more readily 

 than into the capillaries of the air-sacs. 



