179 



from that in which the ramifications of the bronchiae terminate; air never 

 penetrates in it, except when the tissue of the air cells is ruptured. On 

 such occasions, which are not of rare occurrence, on account of the ex- 

 cessive thinness of the lamina of the air cells of that tissue, the lung 

 loses its form, and becomes emphysematous. Haller estimates at about 

 the thousandth part of an inch, the thickness of the parietes of the air 

 cells, and as the extreme ramifications of the plilmonary vessels are dis- 

 tributed on these parieres, the blood is almost in immediate contact with 

 the air. There can be no doubt, that the oxygen of the atmosphere acts 

 on the blood, under such circumstances, since it alters its qualities, and 

 communicates to it a florid red colour, when enclosed in a pig's bladder, 

 and placed under a vesr.el filled with oxygen gas. 



LXXVI. Every time the chest dilates, in an adult, there enter into 

 the lungs, between thirty and forty cubic inches of atmospherical air*, 

 consisting, when pure, of seventy-three parts of azote, twenty-seven of 

 oxygen, und one or two parts in the hundred, of carbonic acidf. 



When the air has been exposed, for a few moments, in the pulmonary 

 tissue, it is expelled by the effort of expiration, but it is diminished in 

 quantity, and is reduced to thirty-eight inches. Its composition is no 

 longer the same: it contains, it is true, 0,79 of azote; but the vital portion 

 fit for respiration, the oxygen, has undergone a great diminution, its 

 proportion is only 0,14: carbonic acid forms the remaining seven hun- 

 dreths, and there are sometimes found one or two pars of hydrogen. It 

 is besides affected by the addition of an aqueous vapour, which is condensed 

 in cold weather, as it escapes at the mouth and nostrils. It is called the 

 humour of the pulmonary transpiration. These changes, compared to 

 those which the blood experiences in passing though the lungs, clearly 

 show a reciprocal action of this fluid and of the oxygen of the atmosphere. 

 The dark venous blood which coagulates slowly, and which then disen- 

 gages a considerable quantity of serum abounding in hydrogen and carbon 

 and of a temperature of only thirty degrees, yields its hydrogen and car- 

 bon to the oxygen of the atmosphere, to form carbonic acid and the pul- 

 monary vapour; and as oxygen cannot enter into these new combinations, 

 without parting with a portion of caloric which keeps, it in a state of 

 gas, the blood acquires this warmth, which is disengaged the more rea- 

 dily, according to the ingenious experiments of Crawford, as by parting 

 with its hydrogen and carbon, its capacity for caloric increases in the pro- 

 portion of 10 : 1 1.5. 



* Some physiologists think that the quantity of air inspired is much less considera- 

 ble. Professor Gregory, of Edinburgh, states, in his public lectures, that scarcely 

 two inches of air enter into the lungs, at each inspiration. It may be proved, how- 

 ever, that this calculation is inaccurate ; either by drawing- a full inspiration, as was 

 done by Mayosv, at the expense of a cei-tain quantity of air contained in a bladder, or 

 by breathing 1 into a vessel connected with a pneumatic apparatus the air taken in, by 

 drawing- a deep inspiration. Or else one may inflate the lungs of a dead body by 

 adapting to the trachea, a stop-cock connected with a curved tube to receive the air 

 under a vessel of the same apparatus. Various means have been employed to mea- 

 sure the capacity of the chest. Boerhaave placed a man in a tub containing water 

 above his shoulders, he then made him take a deep inspiration, and measured the 

 height at which the fluid rose from the dilatation of the chest. Keill injected water 

 into the chest of a dead body. Lastly, it has been proposed to inject the bronchial 

 tubes and the lobular tissue into which they terminate, with fusible metal consisting of 

 eight parts of pewter, five of lead, three 'of bismuth, to which may be added one of 

 mercury. Author's Note. 



t See APPENDIX, Note W, for observations on the changes induced on the air, 

 and on the blood, by respiration, 



