220 RESPIRATION. 



vapours of phosphorous acid stream from the mouth and nostrils, 

 what would hardly have occurred if the acid had been formed 

 in the vessels, as it would probably have remained in solution in 

 the blood, not being volatile. The phosphorus was probably 

 excreted from the vessels in minute subdivision, and united with 

 the oxygen of the atmosphere upon coming in contact with it, 

 producing phosphorous acid ; and the same may be imagined re- 

 specting the carbonic. n There can be no reason to adopt this 

 hypothesis on account of the supposed difficulty of the air and 

 blood acting upon each other through the vessels, because we 

 saw in p. 149. that they do so, through moistened bladder, out 

 of the body. 



The well-known secretion and absorption of air in membranes, 

 shown by the existence of air in the air-bladder of fish, the sudden 

 formation of air in the alimentary canal in disease, the absorp- 

 tion of air in emphysema, and the occurrence of emphysema 

 without injury of the lungs ; the separation of azote and carbonic 

 acid from the lungs when hydrogen is breathed, and the absorp- 

 tion of azote and of oxygen, in the experiments of Dr. Edwards, 

 prove the possibility of the oxygen being absorbed, and the car- 

 bonic acid secreted. 



Lavoisier at one time, and La Grange and Hassenfratz long 

 ago, contended that the carbonic acid is generated in the cir- 

 culation, and given off in the lungs, and the oxygen absorbed. 



Dr. Edwards also argues that, since so much carbonic acid is 

 given out from the blood in the respiration of pure hydrogen, 

 and that, since the quantity given out in hydrogen is as great as 

 is observed in common air, there can be no reason to doubt that, 

 in common air, the carbonic acid proceeds from the same source 

 as in hydrogen, viz. passes from the blood ; more especially as 

 carbonic acid exists largely in the blood : and that the oxygen, 

 therefore, must pass into the blood. These arguments are, in my 

 mind, irresistible. But whether mere carbon leaves the blood 

 and forms carbonic acid with the oxygen externally to the vessels, 

 as in the former theory, or the oxygen unites with, and the car- 

 bonic acid separates from, the blood, as in the latter, much of the 

 affair would appear chemical, neither all the carbon nor all the 

 carbonic acid gas to be secreted; because it has long been known, 



n Dr. Thomson's Annals of Philosophy. 1819. 



o See a case related by Dr. Bail He, in the Transactions of a Society for the 

 Improvement of Medical and Chemical Knowledge , vol. i. 



