GASES OE THE BLOOD. 757 
similar to those of combustiorij but, biassed by his belief in an old theory, he 
concluded that the removal of " phlogiston " turned venous into arterial blood, 
and fur this purification respiration was accessary. For many years there 
were two hypotheses t<> account fur the effect of respiration on the blood. 
According to the one, which originated apparently with Black, 1 and was 
accepted by Priestley, Lavoisier,'-' and Crawford, 3 the oxygen in the inspired air 
combined with the carbon in the venous blood of the lungs, and formed 
carbon dioxide, which was discharged; whereas, according to the other 
hypothesis, proposed by Le Grange, 4 the oxygen was absorbed by the blood, 
and, during the course of the so-called systemic circulation, combined with 
carbon to form carbon dioxide, which was liberated when the blood again 
reached the lungs and took up a fresh supply of oxygen. 
Notwithstanding the experiments of Spallanzani "' and of Edwards, 
which proved that snails, frogs, and kittens continued to give out carbon 
dioxide in an atmosphere of hydrogen, the view that oxidation took place 
in the blood was held until recent times, when the work of Pnliger and 
his pupils showed conclusively that the tissues were the important seat of 
combustion. 
According to Bohr, 7 the tissues of the lungs have a further function than 
that of simply absorbing and discharging gases ; they are said to be able to 
form carbon dioxide from substances brought to them from other parts of the 
body. Thus Bohr and Henriques 8 found that the lungs supplied 68 per cent, 
of the respiratory metabolism. It must be pointed out that in many of the 
experiments upon which this conclusion is based, the operative procedure was 
exceedingly severe, and the condition had no approximation to the normal; 
further, the results are not supported, in fact are contradicted, by the 
numerous experiments on internal respiration. 
The effect of respiration upon the blood is best studied by a com- 
parison of the gases contained in venous blood taken from the right 
ventricle, and in arterial blood taken from the carotid artery. 
The gases of the blood..— Methods for the extraction and esti- 
mation of the gases of the blood. — Historical. — The first demonstration 
of the presence of gases in the blood was made by Boyle 9 in 1636; he 
showed that, when fresh defibrinated blood was exposed to the vacuum of 
an air-pump, gas was given off. These particles of gas Mayow, 10 in 1674, 
considered to be nitro-aerial gas, that is, oxygen. The next important observa- 
tion was that made by Priestley, 11 who noticed that blood placed in an 
atmosphere of hydrogen or nitrogen gave off oxygen. Girtanner 12 observed 
the same effect with nitrogen. In 1799, Humphry Davy 13 found that 
twelve volumes of arterial blood, when heated to 93°, gave off IT volume of 
carbon dioxide, and 0*7 volume of oxygen. 
Nasse, 14 in 1816, proved that blood gave up oxygen to an atmosphere of 
I " Lectures on Chemistry," edit, by Kobison, Edinburgh, 1803. 
"Hist. Acad. roii. d. sc., Paris, 1777, 1789, 1790. 
3 "On Animal Heat," 2nd edition, 1788. 
4 Hassenfratz, Ann. dechim,, Paris, 1791, tome ix. p. 275. 
5 " Mem. sur la respiration," trad, par Senebier, 1803. 
6 " De Finfluence des agens physiques sur la vie," Paris, 1824. 
7 Skandin. Arch. f. Physiol., Leipzig, 1891, Bd. ii. S. 236. 
* C entralll. f. Physiol., Leipzig u. Wien, 1892, S. 225; Com.pt. rend. Acad. d. sc, 
Paris, 1892, tome cxiv. p. 1496. 
9 "Nova experimenta pneumatica respirationem spectantia," Genevae, 1636. 
10 "Tractatus quinque," Oxonii, 1674. "Opera omnia," Hagae Com., 1681, p. 133. 
II Phil. Trans., London, 1776, pt. 1, p. 226. 
12 Hassenfratz, Ann. de chim., Paris, 1791, tome ix. p. 275. 
13 Ann, d. Phys. u. Chem., Leipzig, 1803, Bd. xii. S. 574, 593. 
14 Deutsche Arch. f. d. Physiol., Halle, 1816, Bd. ii. S. 195, 435. 
