THEOUY OF RESPIRATIOK. • %$ 



lungs t he has even rendered it very probable that the air is 



not decompofed, but thai it is abforbed unaltered by the 



blood J that it is decompofed during circulation ; and ihat the 



ulelels portion of azot is again given out. The following Mr. Davy ap- 



fadts are in lupport of this opinion : •* When the gafeous ^^^icleP^^'J^^'^^j^^^^*^ 



of azot is refpired, its quantity is diminiftied, carbonic acid with the oxigen, 



ras is evolved as ufual, and a quantity of azot makes its ap-**^' . 



• ^ ^ n r 1 • r. Fads from the 



pearance. Now as this azot did not exilt leparately, it muftrefpirationof ox. 



have been produced by the decompofuion of the gafeous ox-^*^' «f ^2^t. 

 ide of azot ; but its quantity being much lefs than the azot 

 contained in the oxide of azot which had difappeared, it 

 follows that a part of this laft gas had been abforbed unaltered ; 

 and if a part, why not the whole ? In that cafe the azotic gas 

 muft have been feparated from I he blood by the fubfequent 

 decompofition of the oxide of azot abforbed *." Atmofpheric 

 air is compofed of exactly the fame ingredients as the oxide 

 of azot, merely in different proportions, and in a ftate of lefs 

 intimate chemical combination. It is moreover natural to alk,Oxigen aJone b 

 that if oxigen were alone abforbed by the blood, why (hould il"Jf J^°f " f**'' 

 not anfwer the fame purpofes as air ? It is well known that 

 this gas cannot be refpired for a length of time without pro- 

 ducing fatal confequences ; but even when i( is refpired, the 

 •luantity (of oxigen) which difappears is much fmaller than Much lefs Is ab- 



when a like quantity of atmofpheric air is breathed for the^°[^"* ^."l" 

 - iTV T^ 1 • I r II • . when a hke 



lame time. Mr. Davy has given the roilowmg expernne«t mquantity of ac- 



proof of this fa6t : He breathed 182 cubic inches of oxigen "^''^P*^^"*^'**'^ is 

 gas for half a minute, ll.4c. inches difappeared; whereas 

 when the experiment was repeated under the fame circum- 

 fiances with atmofpheric air, the quantity abforbed amounted 

 to 15.6 cubic inches. 



It was firft obferved by Lower, that the colour of venousLower flrft ob- 

 blood, which is dark reddifli purple, was converted into the^^/"^^** ^^^ 

 florid (carlet colour of arterial blood, in its patfage throughj„^vem)us b^ood 

 the lungs. The phenomena of refpiratlon, however, ftlll re-^y refpirationw 

 mained unexplained, until Dr. Prieftley publiflied his experi- 

 ments on the changes produced in venous and arterial blood 

 when put in contad with certain gafeous bodies. ♦' f He ob- Prieftley ftewed 

 ferves. that having introduced pieces of the craflaraentum of^^^""f*' ^^** 



the ablorptieji of 

 oxigen* 

 . * Thomfon*s Syftem of Chemiftry, Vol. IV. page TIP. 



t Prieftley on Air, Vol. III. jxige.TU 



Ct 2 <oaguIftte4 



