342 RESPIRATION. 



more oxygen in the blood (which was not expended in the formation 

 of carbonic acid) than in respiration in ordinary air. The experi- 

 ments of Allen and Pepys exhibit, moreover, no inconsiderable 

 exhalation of nitrogen. Sir Humphrey Davy's experiments (ac- 

 cording to which most of the vital functions are performed with 

 augmented energy after the prolonged inhalation of oxygen) are 

 worthy of being carefully repeated with such improved means as 

 Lespasse* has lately employed in his observations. 



The respiration of air richer in carbonic acid than the ordinary 

 atmosphere, and the repeated inspiration of air which had already 

 been expired, have been made the subject of numerous investi- 

 gations. Marchand found that frogs which had been suffered to 

 breathe in closed vessels, developed less carbonic acid and inhaled 

 less oxygen towards the close of the experiments than at the 

 beginning, and that at length they absorbed little more oxygen 

 than was necessary for the formation of carbonic acid. The 

 experiments made by Legalloisf on animals, present results differ- 

 ing so essentially from those obtained by other observers, that 

 one scarcely knows how far to trust them. The following fact 

 seem, however, to possess some degree of probability. A larger 

 amount of nitrogen is excreted in an atmosphere rich in carbonic 

 acid than in the ordinary air, and when the air is very richly 

 charged with carbonic acid some of this substance is even absorbed 

 by the blood; the absorption of oxygen is in that case pro- 

 portionally small. 



Davy's experiments prove that pure carbonic acid cannot be 

 inhaled, as the glottis spasmodically obstructs its passage ; 60 or 

 even 40^ of carbonic acid are sufficient to render an atmosphere 

 unfit for respiration, although air less densely charged with this 

 acid may be respired for some time without producing any 

 injurious effects, and the danger induced by its prolonged respira- 

 tion depends less upon the actual amount of carbonic acid than 

 upon the insufficient supply of oxygen conveyed to the lungs by 

 such an atmosphere. 



It has been shown by Legallois* experiments on guinea pigs, 

 that in air which is richer in nitrogen than the atmosphere, 

 nitrogen is absorbed and less carbonic acid exhaled ; the absorp- 

 tion of oxygen appears to be relatively greater than in atmo- 

 spheric air. 



The inhalation of pure nitrogen gas is speedily followed by 



* Compt. rend. T. 22, p. 1055. 



t Exp. sur le principe de la vie. Paris, 1812. 



