7 6o CHEMISTR Y OF RESPIRA TION. 
end of the blood-receiver, as far as the closed screw-clip. Before the 
insertion of the cannula, the end of the rubber tube is compressed with 
the fingers to exclude the air within it. A sufficient quantity of blood 
is now withdrawn by opening at the same time the screw-clip and the 
clip placed on the blood vessel of the animal. The blood is defibrinated 
by shaking it with the mercury left within the blood-receiver for that 
purpose, and the latter is then again weighed. The weight of the sample 
of blood is then obtained. The blood-receiver is next affixed once more to the 
tube (E), in the dependent position shown in the figure, and the tube (E) is 
exhausted. Finally, the screw-clip between E and the blood-receiver is 
opened, and the gases are withdrawn and collected in the eudiometer. Since 
the blood-receiver hangs freely from the tube (E) by means of a piece of 
rubber tubing, it can be both immersed in warm water, and shaken to facilitate 
the complete escape of the gases. The bulbous form of the blood-receiver 
prevents the blood from frothing over into the pump ; and if the action 
becomes too violent, it can be immediately allayed by pouring a few drops 
of warm water on to the tube (E). The bubbles are thereby driven back into 
the receiver, and the pump is never fouled. The tap (D) is so manipulated 
that the gases only, and not the water which condenses in the reservoir (B), 
are driven over into the eudiometer. The water is returned back into the 
blood-receiver. Three or four exhaustions are sufficient to extract all the gases 
from about 10 grms. of blood." 
Methods of gas analysis cannot be described here; it is only necessary to refer 
the reader to the works of Bunsen, Hempel, and others 1 upon this special subject. 
In the extraction of the gases of the blood methods are employed which 
favour the dissociation of those gases which are present in loose chemical 
combination, and also liberate the gases present in a state of simple solution. 
These conditions are fulfilled by exposure to a vacuum, by warming and 
agitating the blood. The addition of a weak acid favours the evolution of the 
carbon dioxide. The effect of these different procedures upon the dissociation 
of oxyhaemoglobin will be considered later ; here it is only necessary to recall 
the fact that the coefficient of absorption of gases in fluids diminishes with an 
increase of temperature, and becomes nil when the boiling point of the fluid is 
reached. 
For the quantitative estimation of the oxygen contained in blood, Claude 
Bernard 2 introduced a method based upon the stronger affinity shown by 
carbon monoxide than by oxygen for haemoglobin. The blood is shaken with 
double its volume of carbon monoxide, which drives out the oxygen from its 
combination with hsenioglobin. An analysis of the gas collected shows the 
percentage of oxygen. Nawrocki 3 has made comparative analyses Avith this 
method and with the ordinary blood pump, and the results are practically the 
same. If, however, the blood is left in contact with the carbon monoxide for 
longer than twenty-four hours, some of the gas combines with oxygen to form 
carbon dioxide, and thus the amount of oxygen is diminished. 4 It is possible 
that the carbon dioxide formed in these cases is due to putrefaction. 
The differences in the gases of arterial and venous blood. — 
A comparative examination of the gases contained in arterial and venous 
blood is necessary for the estimation of the qualitative and quantitative 
changes which occur during external and internal respiration. 
The gases of arterial blood. — The chief results obtained by 
1 Bunsen, " Gasometrische Methoden," 1857; "Gasometry," Roseoe's transl., London, 
1857; cf. also Gamgee, op. cit., pp. 206-215; Hempel, " Gasanalytische Methoden"; 
Geppert, " Die Gasanalyse," 1885. 
2 " Lecons sur les liquides de l'organisme," Paris, 1859, tome i. p. 365 ; ii. p. 427. 
3 Stud. d. physiol. Inst, zu Brcslau, Leipzig, Bd. ii. S. 144. 
4 Bernard, loe. cit., Pokrowsky, VircTww's Archiv, 1866, Bd. xxxvi. S. 482. 
