GASES OP THE BLOOD. 757 



similar to those of combustion, but, biassed by his belief in an old theory, he 

 concluded that the removal of " phlogiston " turned venous into arterial blood, 

 and for this purification respiration was necessary. For many years there 

 were two hypotheses to account for the effect of respiration on the blood. 

 According to the one, which originated apparently with Black, 1 and was 

 accepted by Priestley, Lavoisier, 2 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 5 and of Edwards, 6 

 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 Pfliiger 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 I'l volume of 

 carbon dioxide, and 0*7 volume of oxygen. 



JNasse, 14 in 1816, proved that blood gave up oxygen to an atmosphere of 



1 "Lectures on Chemistry," edit, by Robison, Edinburgh, 1803. 

 3 Hist. Acad. roy. d. sc., Paris, 1777, 1789, 1790. 



3 " On Animal Heat," 2nd edition, 1788. 



4 Hassenfratz, Ann. de chim., Paris, 1791, tome ix. p. 275. 



5 "Mem. sur la respiration," trad, par Senebier, 1803. 



6 "De 1'influence des agens physiques sur la vie," Paris, 1824. 



7 Skandin. Arch. f. Physiol., Leipzig, 1891, Bd. ii. S. 236. 



8 CentralU. f. Physiol. , Leipzig u. Wien, 1892, S. 225; Compl. rend. Acad. d. sc., 

 Paris, 1892, tome cxiv. p. 1496. 



9 "Nova experiments pneumatics respirationem spectantia," Genevse, 1636. 



10 "Tractatus quinque," Oxonii, 1674. "Opera omnia," Hagae Com., 1681, p. 133. 



11 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 Deutsches Arch. f. d. Physiol., Halle, 1816, Bd. ii. S. 195, 435. 



