RESPIRATION. 219 



1. That if an animal is made to breathe oxygen mixed with ^ 

 of azote, azote is discharged in abundance, as was found by Allen 

 and Pepys, so that, when there is little or no azote to be absorbed, 

 its exhalation at once shows itself; and we may conclude that in 

 common respiration its exhalation may be as great, but not ob- 

 servable, because nearly an equal quantity is absorbed : 



2. When a mixture of oxygen and hydrogen was employed by 

 those chemists, and pure hydrogen by Dr. Edwards, not only was 

 a large quantity (much exceeding the bulk of the animal) given 

 out, but a considerable quantity of hydrogen was absorbed, in 

 Dr. Edwards's experiment equal to the azote given oute, proving 

 that exhalation and absorption can proceed together : and he asks 

 why, if hydrogen is absorbed, not much more so azote, which is 

 more fit for respiration and the support of life ? and concludes 

 that its absorption may be as great in common respiration, but 

 not observable because a nearly equal quantity is discharged. h 



Carbonic acid itself is shown by Spallanzani and Dr. Edwards 

 to be exhaled from the lungs independently of the operation of 

 oxygen ; when snails, frogs, fish, or very young kittens, are im- 

 mersed in hydrogen. 



It is satisfactory that Messrs. Allen and Pepys were induced, 

 without any knowledge of Dr. Edwards's researches, to repeat 

 their enquiries, and their results no longer disagree with those 

 of Dr. Edwards. On making birds breathe in atmospheric air, 

 they still found the loss of oxygen equal to the addition of 

 carbonic acid, and the nitrogen unchanged; if in air with an 

 excess of oxygen, a quantity was absorbed beyond what was 

 replaced by carbonic acid, and in its room appeared an equal 

 quantity of nitrogen ; if in a mixture of oxygen, hydrogen, and 

 nitrogen, the oxygen being in the same proportion as in atmo- 

 spheric air, there was no loss of oxygen, but of hydrogen, which 

 was exactly replaced by nitrogen. k 



Mr. Ellis 1 contends that the carbon is excreted by^the pulmo- 

 nary vessels, and unites with the oxygen externally, and Dr. Prout 

 thought this opinion corroborated by the fact m , that, when 

 phosphorus dissolved in oil is injected into the blood-vessels, 



e 1. c. p. 462. h 1. c. 429. sqq. 



1 1. c. p. 437. sqq. k PhU. Tran*. 1829. 



1 An Enquiry into the Changes induced in Atmospheric Air. 1807. Further 

 Enquiries, $c. 1816 



01 Dr. Orfila, Toxicologie Generate, t. i. p. 531. sq. Dr. Magendie had pre- 

 viously found the same result in injecting the solution into the pleura. ~ 

 sur la Transpiration, p. 1 9. 



