RESPIRATION, ORGANS OF. 



271 



point. Carpenter, Qnain and Sharpey, Kirkes 

 and Paget, Kolliker, S. Van der Kolk, Hurting, 

 Adriani, and Schultz describe a pavement epi- 

 thelium on the interior of the air-cells of the 

 lungs ; and the author who has devoted many 

 special examinations to this particular point 

 is now convinced that a fine pavement epithe- 

 lium docs cover these parts which he proposes 

 to distinguish as the " hyaline epithelium" * 

 Messrs. Todd and Bowman, like Rossignol, 

 adopt the views of Mr. Rainey, and teach 

 that the air-cells have no epithelium of any 

 kind. The adjoined is the illustration of the 

 epithelium given by Schroeder Van der Kolk 

 in Adriani's Essay.f 



Fig.219. 



Ultimate cells of the human lung, showing the trabi- 

 cular framework formed by the elastic fibres of the 

 walls, and the hyaline pavement epithelium which 

 lines the interior of the air-cells. (After Schroeder 

 Van der Kolk, quoted by Adriani.) 



By this distinguished observer it is repre- 

 sented under the character of transparent 

 pavement epithelium, the cells of which are 



* In suggesting the word hyaline as a distinctive 

 epithet for this variety of epithelium, I do not wish 

 to be understood as denying, in its component 

 scales, the existence of every form of visible 

 element. The word should be accepted in a com- 

 parative sense, as signifying that their nuclei and 

 granules are less declared than those of any other 

 description of epithelium. 



f This figure is thus described by Adriani : 

 " Alveoli constant membrana subtilissima structure 

 carente, qua?, autem membrana mucosa tegitur epi- 

 thelio pavimentoso (plaat epithelium') admodum pel- 

 lueiilo, in quo potissimum ope acidi acetici nuclei 

 conspiciuntur; propter singularem autem pelluci- 

 ditatem srepe difficile est, illud epithelium rite dis- 

 tiuguere ; vid. fig. 12. nostram, ubi ad alveolorum 

 parietes conspicitur. Cellulte conica? ciliatie qua? in 

 bronchiolis minutis adhuc conspiciuntur, in alveolis 

 penitus deficiunt ; hajc membrana cum epithelio 

 pavimentoso obtegit vasa sanguifera per alveolorum 

 parietes ducta ; propter singularem tenuitatem im- 

 bibitio atqne absorptio per hanc membranulam 

 facillime pcrfici posse facile intelligitur." Op. cit. 

 p. 61. 



furnished with a nucleus and minute granules 

 They are adjusted accurately, as a single la\er, 

 edge to edge. The description given by Kol- 

 liker coincides with the preceding.* 



Fig. 220. 



A thin section of a few air-cells from the human lung, 

 viewed by transmitted light. (After Kolliker.) 

 a, epithelium lining the air-cells ; b, elastic tissue 

 arching over and between the cells ; c, the flat wall 

 of a cell, showing the scanty distribution of elastic 

 fibres over this part of the cell. 



By Kolliker the cells of this epithelium (a, 

 y?.2-20.) are stated to consist of polygonal par- 

 ticles of from 1 1600th to 1 2250th of an inch 

 in diameter, and from 1 2800th to I 3800th 

 of an inch in thickness. They repose imme- 

 diately upon the fibrous layer. They are 

 normally shed; though not readily detected 

 in health, it is easy to discover these epithelia 

 in disease. This epithelium lines every part of 

 the air-passages and cells except the bronchi. 

 These latter tubes are furnished with a thick 

 layer of ciliated epithelium, which, as formerly 

 stated, terminates abruptly at the commence- 

 ment of the intercellular passages. It may 



* The following passage in the Microscopic Ana- 

 tomy of Kolliker refers to the figure cited in the 

 text. " Das Epithelium der Lungenblaschen ist 

 kein flimerndes, wie man friiher ziemlich allge- 

 meine annahm, sondern ein gewb'hnliehes Pflaster- 

 epithelium, das mit polygonalem Zellen von 0-005 

 0-007'" Durchmesser und 0-003 0-004'" Dicke in 

 einfacher Lage unmittelbar auf der Faserhaut der 

 Luftblaschen aufsitzt. Die Zellen sind alle kern- 

 haltig, und haben meist ausserdem der Trachea 

 und der Bronchien auzunehmen, dagegen kb'nnen 

 allerdings mehr zufiillig oder dann in Krankheiten 

 der Luftwege einzelne Elemente desselbcn dcm 

 Bronchialschleime sich beimengen. Beim Menschen 

 fallen diese Zellen ungemein leieht ah und liegen 

 dan frei in den Luftblaschen und fcinsten Bronchien, 

 doch kann man fast in jeder Lunge, wenigstens in 

 einzelnen Alveolen diese'lben nocli in situ sehen und 

 bei eben getodtetcn Thieren bietet bei Beobachtung 

 der Lagerung derselben nicht die gcringsten Schwie- 

 rigkeiten dar." Op. cit., p. 315. 



