THE LUNGS. 145 



communicate laterally with one another, as the cells of the 

 bones, but only with the ramifications of the bronchia, to which 

 they respectively belong. Recent preparations, however, have 

 induced me to abandon this idea, arid to conclude that the efells 

 of the lobules individually communicate, but not those of dif- 

 ferent lobules. I have succeeded in proving this by distending 

 the air cells with tallow, and, after the lung was dried, by re- 

 moving the tallow with spirits of turpentine. This process 

 shows the cells of their natural size, and communicating freely. 

 A very small portion of a lung of either the human subject 

 or the calf kept inflated and dried shows the same unequivo- 

 cally. 



In tracing the terminations of the bronchia, in the substance 

 of the lungs, the parietes of these canals are observed to become 

 very thin, and especially after the cartilaginous structure has 

 ceased. The ramifications seem then to be composed almost 

 entirely of muscular fibres, and a lining of mucous membrane ; 

 the latter is smooth, polished, and so thin that it is a mere film, 

 about the thickness and transparency of the peritoneum, where 

 it covers a small intestine. Longitudinal folds may still be 

 traced in the length of the mucous membrane, and, with the aid 

 of a lens, mucous follicles are very perceptible, in innumerable 

 quantities all over it. It may also be remarked, that the bronchia 

 do not end by a regular succession of proportionately finer and 

 finer branches ; but that a bronchial trunk, of some lines in 

 diameter, sends off in different directions to the contiguous lo- 

 bules, branches about the size of a bristle, which are followed 

 with much difficulty, owing to their collapsing: the probability 

 is, however, that each one of these branches belongs to a lobule 

 and discharges into its cells, in a. manner resembling a blow- 

 pipe fixed to the side of a small piece of sponge. In my pre- 

 parations, these terminating tubes of the bronchia, the size ol 

 bristles, are seen very distinctly ; but there is no appearance 

 of the penicillous arrangement, which would be apparent if 

 each air cell had its own specific branch of the bronchus run- 

 ning to it. 



Besides the ramifications of the bronchia, the substance of the 

 lungs is composed of numerous blood vessels and lymphatics, and 

 is well supplied with nerves. 



The blood vessels are of two kinds, the pulmonary and the 



VOL. II. 14 



