RESPIRATION, ORGANS OF. 



269 



Weber, from the ^ to the T V of an inch. 

 It has been calculated by M. Rochoux that 



Fig. 217. 



Pleural surface of the human lung, indicating the 

 lobules in shaded outline, and the air-cells a, a. 

 (After Adriani.) 



as many as 17,790 air-cells are grouped 

 round each terminal bronchus ; and that their 

 total number in the lungs amounts to no less 

 than six mil/ions. The dimensions of the air- 

 cells given by M.Moleschot*, are very much less 

 than those of Rainey and Kolliker. Accord- 

 ing to the former observer, they range from 

 T _th to TaV^th of an inch : those of Car- 

 penter and Kolliker correspond with those of 

 Weber already stated. They continue to 

 increase in size from birth to old age, and 

 present in man a greater capacity than in 

 woman. Dr. W. Addison supposed that the 

 air-cells did not exist before birth, that they 

 were mechanically formed by the first act of 

 inspiration, and that the foramina between 

 the cells were really ruptured partitions 

 caused by the pressure of the atmosphere. 



Fig. 218. 



Ultimate pulmonary tissue from a foetus three months 



old. (After Harting, quoted by Adriani.^) 

 a, a, a, primitive " infundibula," of which the 

 parietes are as yet composed only of minute oval 

 cells (c) ; b, b, b, elastic tissue occupying the inter- 

 vals between the infundibula, exhibiting the nuclei 

 of its cells. 



* Op. cit. 



It was, however, first proved by Mr. Rainey, 

 and by Professor Harting more lately, that 

 they exist nearly as perfect in contour before 

 as after birth. Neither the form, the num- 

 ber, nor the disposition of the air-passages 

 and cells can any longer be held as the off- 

 spring of chance, but as the nicely adjusted 

 products of marvellous foresight and design. 



The preceding statement will enable the 

 reader to understand the sources of the dif- 

 ferences by which the views of different writers 

 upon the structure of the lungs are marked. It 

 is easy to make a " labyrinth," a " passage," or 

 a "group of vesicles," or " a funnel-shaped ar- 

 rangement of cells," out of the complex ap- 

 pearance which a section of an inflated and 

 dried lung presents. It is important to observe 

 that the classification of the cells into the pa- 

 rietal and terminal, as suggested by Rossignol, is 

 calculated to lead to a false idea as to the real 

 arrangement of the air-cells within the lo- 

 bule. The capsule of the lobule encloses a 

 pear-shaped space ; but this is not the infun- 

 dibulum of Rossignol. This ingenious author 

 applies this term to those parts which Mr. 

 Rainey and Dr. W. Addison have distin- 

 guished as the air-passages surrounded and 

 terminated by secondary passages and air- 

 cells. The septa bearing alveoli which pro- 

 ject everywhere into the funnel of Rossig- 

 nol, render the word parietal, as applied to 

 them, altogether unmeaning. Every recent 

 observer admits that the air-cells open every- 

 where into one another, such that the air 

 entering one intercellular passage at one part 

 of the lobule would traverse its entire extent 

 through the intervening labyrinth of cells, and 

 return through another air-passage into the 

 same peduncular bronchus. 



When two sides of two contiguous air- 

 passages or cells come into opposition, the 

 resulting partition is not composed of two 

 layers, but one. If the cells were formed 

 by the protrusive force of the air in enter- 

 ing in the first act of inspiration, such par- 

 titions would, of mechanical necessity, consist 

 of two layers : they are, however, formed 

 by an act of organisation. This curious 

 and distinctive fact in the history of the 

 human and the mammal lung wBl be again 

 referred to. As the partitions of the cells 

 are organised before birth, it follows that 

 the geometrical outline of each cell must be 

 determined before the first act of inspiration. 

 The same argument applies to the foramina 

 between the cells. They are not accidental 

 perforations ; they are definitively and de- 

 signedly organised orifices, and are sustained 

 in a permanently patulous state by an arch- 

 like arrangement of elastic fibres, which will 

 be afterwards described. 



As the air-cells of the lungs of mammals 

 generally bear no proportion in size to that 

 of the body of the animal, so in the human 

 subject there is no relation between the di- 

 mensions of these cells and the stature of the 

 body ; and it is probable that no estimate can 

 be formed of the vital capacity of the lungs 



