ABSORPTION THROUGH THE LUNGS. 5t>9 



a. It li:is recently been attempted, by Mulder and others, to account for the change of hue 

 under the influence of carbonic acid, oxygen, and saline matter, by a change of form in the 

 red corpuscles ; which are supposed to be bi-concave and reflecting in bright coloured blood, 

 and bi-ennvex and refracting in blood presenting the venous tint. But the supposition is not 

 borne out by minute and careful observations on the forms of the corpuscles, nor by varied 

 experiments on the effects of re-agents. As Dr. G. 0. Rees has shown, the blood-corpuscles 

 maybe changed in form, without any consequent change of colour; whilst, on the other 

 hand, the blood is reddened by saline solutions, whether they produce endosmose or exos- 

 mose in the red corpuscles, thus either filling or emptying them, and rendering them either 

 bi-convex or bi-concave. 



773. Exhalation and Absorption by the Lungs. The alteration in the 

 proportions of its usual gaseous ingredients, is by no means the only change 

 which the Blood undergoes in the Lungs. It parts also, with a considerable 

 amount of water, in the form of vapour; this usually contains a certain pro- 

 portion of animal matter; and it is sometimes charged with volatile substances, 

 which have been elsewhere introduced into the blood, or which have been 

 formed during its assimilation. It may also absorb from the atmosphere vola- 

 tile matter diffused through it. Both these changes are probably to be ex- 

 plained upon simple physical principles ; being dependent on the exposure of 

 the blood to the atmosphere, over a very extensive surface, and through a 

 membrane of great permeability. Of the fluid ordinarily exhaled with the 

 breath, a part doubtless proceeds from the moist lining of the nostrils, fauces, 

 &c. ; but it is indisputable that the greater proportion of it comes from the 

 lungs, since, when the respiration is entirely performed through a canula intro- 

 duced into the trachea, the amount of watery vapour which the breath contains, 

 is still very considerable. The quantity which thus passes off is by no means 

 trifling; probably between 16 and 20 ounces in the twenty-four hours. It is 

 not so liable to variation under the influence of temperature, the movement of 

 the surrounding air, and other similar causes, as is the cutaneous transpira- 

 tion ; for air, which has found its way into the air-cells of the lungs, is, 

 under almost all circumstances, nearly the same in regard to such conditions, 

 and becomes charged with that amount of watery vapour which saturates it at 

 the temperature of the body. It is considered by Dr. Prout, that the principal 

 source of this vapour is not the blood properly so called, but the chyle and 

 lymph which have just been introduced into it from the thoracic duct; a loss 

 of a portion of their fluid being required, to give them sufficient concentration. 

 A process very analogous takes place in Plants; for a very large proportion of 

 the water taken up in the crude sap, is parted with in the leaves. But it is 

 probable that a part, at least, of the water thrown off by the lungs is generated 

 by the union of Oxygen and Hydrogen during the course of the Circulation.. 



774. The fluid thrown off from the Lungs is not pure water. It holds in 

 solution, as might have been expected, a considerable amount of carbonic acid, 

 and also some animal matter; the exact nature of the latter, which, according 

 to Collard de Martigny, constitutes about 3 parts in 1000, has not been ascer- 

 tained. If the fluid be kept in a closed vessel, and be exposed to an elevated 

 temperature, a very evident putrid odour is exhaled by it. Every one knows 

 that the breath itself has, occasionally in some persons, and constantly in 

 others, a fetid taint; when this does not proceed from carious teeth, ulcerations 

 in the air-passages, disease in the lungs, or other similar causes, it must result 

 from the excretion of the odorous matter, in combination with watery vapour, 

 from the pulmonary surface. That this is the true account of it seems evident, 

 from the analogous phenomenon of the excretion of turpentine, camphor, alco- 

 hol, and other odorous substances, which have been introduced into the venous 

 system, either by natural absorption, or by direct injection; and also from the 

 suddenness with which it manifests itself, when the digestive apparatus is 

 slightly disordered. 



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