760 CHEMISTR Y OF RESPIRA TION. 



end of the blood-receiver, as far as the closed screw-clip. Before the 

 insertion of the canmila, 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 is now withdrawn by opening at the same time the screw-clip and the 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 opened, and the gases are withdrawn and collected in the eudiometer.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 oxyhsernoglobin 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 hemoglobin. An analysis of the gas collected shows the 

 percentage of oxygen. Nawrocki 3 has made comparative analyses with 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, " Roscoe's transl. , London, 

 1857; cf. also Gamgee, op. cit., pp. 206-215; Hempel, " Gasanalytische Methoden"; 

 Geppert, " Die Gasanalyse," 1885. 



2 " Le9ons sur les liquides de 1'organisme," Paris, 1859, tome i. p. 365 ; ii. p. 427. 



3 Stud. d. physiol. Inst. zu Breslau, Leipzig, Bd. ii. S. 144. 



4 Bernard, loc. cit., Pokrowsky, Virchow's Archiv, 1866, Bd. xxxvi. S. 482. 



