RESPIRATION. 221 



that, when venous blood is exposed to oxygen out of the body, 

 even although covered by a moistened membrane, it becomes 

 florid, and oxygen disappears and is replaced by carbonic acid. 



Since the publication of Dr. Edwards's work, numerous facts 

 have been ascertained, which cause his opinions on these points 

 to be generally received, by proving the possibility of the transfer 

 of oxygen to the blood, and of carbonic acid to the air, even 

 on chemical principles. My friend Dr. Stevens discovered that 

 oxygen and carbonic acid attract each other ; so that, if car- 

 bonic acid is placed at the lower part of a tube, and oxygen 

 above, the acid, though heavier, will ascend and the oxygen 

 descend. Nay, if a vessel filled with carbonic acid be com- 

 pletely closed with bladder, the acid will escape and the bladder 

 be forced in ; while, if it be filled with air and placed in car- 

 bonic acid, the latter will pass through and distend the bladder 

 till it nearly bursts. The tendency to diffusion is universally as 

 the square root of the specific gravity. The subject has been 

 prosecuted by Drs. Mitchel and Faust P ; and they have ascer- 

 tained that both living and dead membranes, and even caoutchouc, 



P American Journ. of the Medical Sciences, No. xiii. 1830. They do not men- 

 tion Dr. Stevens's name, but he had made his observations in the West Indies 

 in 1827 and committed them to paper, and shewn them in England in 1828, in 

 France in 1829, and in America in the summer of 1830, when he mentioned 

 them to the very editor of the Journal of Medical Sciences, who took part in Dr. 

 Mitchel's experiments, which were soon afterwards begun and published before 

 the end of the year. In 1833, also, M. Saigay published (in the Annales des Sc. 

 d'Observat. t. iii. p. 452.) an explanation of the interchange of gases through fluids 

 and porous substances; that each gas maintains an equilibrium outside and 

 inside; so that, when there is less without, it passes forth ; and, when more with- 

 out, it passes in. In this way M. Raspail conceives that the appearance and dis- 

 appearance of all the various gases in respiration, under different circumstances, 

 may be accounted for. (1. c. p. 258. ) There must be, however, a relation be- 

 tween different gases, or nitrogen would be exchanged, as well as oxygen, for 

 carbonic acid, in ordinary respiration. 



M. Dutrochet stated that, if a dense fluid is enclosed in an animal membrane, 

 it attracts a thin fluid placed around the exterior. The passage of the external 

 fluid he called endosmose. If the dense fluid is placed externally, and the thin 

 inside, then the thin fluid passes outwards. This passage he termed exosmose. 

 M. Raspail soon adduced exceptions to this, and showed that the phenomena 

 were merely those of ordinary imbibition : that, if the fluid on one side was of a 

 kind to pass through membrane, and the fluid on the other was not, and the two 

 were of a kind to unite, then the one fluid of course soaked into the membrane 

 and, having soaked into it, united with the other fluid, as soon as the other side of 

 the membrane was reached ; and more followed in its place. (1. c .p. 80* sqq.) 



Q 



