GLAKDS. 93 



these accumulate in the intervesicular partitions, and 

 form likewise the central portions of the trabeculse 

 PL XIX. fig. II. 1). The nature of this membrane 

 explains the great elasticity of the lungs. 



The epithelial lining of the pulmonary vesicles is Epithelium. 

 composed of many-sided cells with very pale outlines, 

 measuring, in mean diameter, ai^th of a line, and 

 having no cilia ; their nuclei are very large (2 ijth of 

 a line) and full of dark granules (PL XIX. fig. II. 2 ; 

 fig. III.). This epithelial layer is found also upon the 

 trabeculse. I have reason to believe that fatty dege- 

 neration of these epithelial cells always constitutes 

 the initial lesion of pulmonary tuberculosis.* 



In tracing the epithelium from the vesicles and ^'nayer epi " 

 lobules into the bronchial tubes, the single layer of 

 cells becomes double, and the number of strata con- 

 tinues to increase as the air-tubes enlarge in calibre ; 



* The existence of an epithelial lining to B the air-cells of the lungs is one 

 of the most recently established facts of histological science. It is denied 

 by recent and high authorities, viz. Kainey (Med. CMr. Trans, vol. xxxii. 

 1849, p. 51 ; and Brit, and For. Med. CMr. Rev. No. xxxii. p. 491), and 

 Todd and Bowman (Phys. Anat., Lond. 1856, vol. ii. p. 391) ; although 

 the latter admits the fact in his article on " Mucous Membranes" in the 

 Cyclopaedia of Anatomy. It is asserted by Carpenter (Human Physio- 

 logy, p. 513, 4th Ed. Lond.), by Quain and Sharpey, Kolliker, Rossignol, 

 Adriani, Schroeder van du Kolk, Schultz (Disqumt. de structured et tex- 

 turd canalium ariferorum, 1850, p. 10) ; Williams (art. Lungs in Cyclo- 

 pedia of Anatomy, 1855) ; Dr. Radclyffe Hall (Brit, and For. Med. CMr. 

 Rev. No. xxx. p. 481) ; Mandl (Anat Micros, vol. ii. p. 327) ; Milne 

 Edwards (Lemons sur la Physiologie, &c., t. ii., p. 326) ; Peaslee (Human 

 Histology, &c., &c., Philad. 1857, p. 579), and Waters (op. cit., p. 159). 

 According to the latter authority it is best seen in a perfectly fresh spe- 

 cimen of lung tissue, and by the aid of acetic acid. According to Kol- 

 liker it is " an ordinary pavement epithelium without cilia, which forms 

 a single layer, and rests immediately on the fibrous coat" of the pulmo- 

 nary vesicles. (Ed.) 



