270 



RESPIRATION, ORGANS OR 



from a calculation of the individual dimensions 

 of the air-cells. It should be observed that the 

 orifices, by which one cell communicates with 

 another, are of the same shape and dimensions 

 as those which exist between the first set of 

 cells and the bronchial tubes ; they can be 

 very distinctly seen by looking down upon the 

 air-cells from the intercellular passages, focus- 

 sing the "microscope at the same time. Since 

 these openings are not necessarily in a straight 

 line, the exact number of cells which com- 

 municate cannot in this manner be, determined; 

 but the number will depend upon the dis- 

 tance which intervenes between any given 

 part; of the bronchial passage and the surface 

 of the lobule : so that when a bronchial 

 passage arrives nearest the surface it will be 

 separated from it only by a single terminal 

 cell. The dimensions of the cells in different 

 animals present many diversities. In the 

 lung of the kangaroo, especially in those parts 

 remote from the surface, the air-cells are 

 very small, and disposed with the greatest 

 irregularity. The lining membrane is also 

 proportionally imperfect, being perforated in 

 many places opposite the areolas of the plex- 

 uses, so as to admit the air passing through 

 them to come into contact with the coats 

 of the vessels, as in the lung of the bird. In 

 this mammal the minuteness of the air-cell 

 is such, that it is too small to contain a single 

 ciliated epithelium (Rainey). In the lung of 

 the rat and mouse the air-cells are still more 

 minute, and certainly many of them are not 

 of a sufficient size to receive even an indi- 

 vidual particle of the dimensions of the bron- 

 chial ciliated epithelium. The air-cells are 

 disposed with the same kind of irregularity, 

 and the pulmonary membrane is deficient, as 

 in the lung of the kangaroo. In the lung 

 of the hare, the air-cells are very small, but 

 perhaps not so much so as in the preceding 

 species. The lung of the rabbit resembles 

 that of the hare, but its air-cells are rather 

 larger. In the lung of the dog the air-cells 

 are larger than in the rabbit ; but still in the 

 more central parts of the lung they are very 

 minute, too minute, indeed, to be capable of 

 having a lining of ciliated epithelium without 

 being wholly unfitted for the purposes of 

 respiration. In the monkey, the air-cells are 

 large, and resemble those in the human lung. 

 In the lung of the sheep and ox they are, upon 

 the whole, about the same size, and very 

 minute in both.* 



The diameter of one of the intercellular 



* As the following passage expresses the views 

 of S. van der Kolk, Harting, Kolliker, as well as 

 that of the writer, Adriani, I append it here at 

 length : 



" Has cavitates antea cellulas dictas, mine Dr. 

 Rossignol alveoles nuncupavit, quod admitti potest, 

 si nemo tantum huic nomini regularitatem mathe- 

 maticam adjung.it, qu;e in alveolario apintn inve- 

 nitur ; in pluribus locis eiiim alveoli infimdibulorum 

 aut rotundi sunt, aut niagis polygonam figuram 

 referunt ; eorum parietes vasis cinguntur minutis- 

 simis, confertissimis, snepe optime materia colorata 

 impletis, et tune rete subtilissimum constituenti- 

 bus. Fibra3 autem elastiea) potissimuni ad mar- 



passages ranges from T i- to ^-i- of an inch, 

 and that of the cells from ^ to ^i_ (Todd 

 and Bowman). In the lung of the calf these 

 cells do not exceed ^1^ By Dr. W. Addi- 

 son they are stated, in the human lung, to 

 measure from TT ! rs . to -ig. of an inch. 



Minute Structure of the Air- Cells. Three 

 anatomical elements enter into the composi- 

 tion of the air-cells : the epithelium, the blood- 

 plexus, and the elastic tissue. The inter- 

 lobular tissue is not here considered. 



1st. The Epithelium of the Air-Passages and 

 Cells. It was first surmised by Dr. Thomas 

 Addison, from the phenomena of the dif- 

 ference between pneumonia and bronchitis, 

 that the air-cells of the lungs must be desti- 

 tute of epithelium. Dr. W. Addison contends 

 that the air-cells "possess an epithelium in 

 form of large round nucleated scales, and from 

 one to fifteen or more nuclei may be counted 

 in a single scale. A great many nuclei without 

 any epithelial envelope may be seen upon 

 them ; but I have never satisfied myself that 

 they possess the ciliated cylinder epithelium so 

 abundant in the trachea a'ncl bronchi."* 



Mr. Rainey denies the presence of epithe- 

 lium of any description on the interior of the 

 air-cells, the vascular plexus being lined only 

 by a " pulmonary membrane." Rossignol is 

 the only subsequent writer who has sup- 

 ported this view : " Neither does the ciliated 

 epithelium lining the bronchial tubes extend 

 into the intercellular passages, and from thence 

 into the air-cells, or rather air-spaces (speak- 

 ing of the bird's lung), but it ceases where 

 the bronchial membrane terminates. In the 

 mammal, but especially in man, in whom the 

 air-cells are very large, the fact of their having 

 no epithelial lining can only be proved by a 

 careful examination of the parts with the 

 microscope, and therefore, with no other 

 means than those of deciding this question, it 

 might always remain sub judice, so long as 

 persons are found who are more ready to 

 confide in the assertions of others than submit 

 to the pains and difficulty of examining the 

 point for themselves."-]- Rossignol says: 

 " Les parois alve'olaires sont formees : 1 par 

 une charpente de fibres qui laissent entre elles 

 des espaces vides on areoles ; 2 par une mem- 

 brane transparente, qui n'offre aucune trace 

 de fibres, qui recouvre la charpente precedente, 

 et remplit les espaces vides." In this passage 

 M. Rossignol has evidently adopted without 

 inquiry the conclusion of Mr. Rainey, with 

 whose writings he seems well acquainted. The 

 opinion of all German and English anatomists 

 is now finally formed with reference to this 



gines septorum, quibus alveoli constitnuntur, de- 

 currunt, tamen uti jam monuimus, nonnullas per 

 parietes ipsos etiam decurrunt. Vasa capillaria 

 majora hac tela sustinentur. In ipsis parietibus 

 infundibulorum alveoli inveniuntur, in ipsos bron- 

 chiolonim ramos sese ostendentes ; Rossignol, qui 

 etiam illos vidit, eos alveolos parietales vocavit ; nos 

 autein, antequam ejus commentatio fuerat edita, 

 cellulas parietales vocavimus." P. 43. Op. cit. 



* Phil. Trans. 1842, part i. p. 1C2. 



f Rainey, Med. Chir. Trans, vol. xxxii. 1849. 



