THE CHEMISTRY OF RESPIRATION 



1177 



argon. Argon is present only in insignificant quantities, about '04 

 volume per cent. The nitrogen also forms only between one and 

 two volumes per cent, and is present in the same proportion in both 

 arterial and venous blood. The amounts of oxygen and carbon 

 dioxide in these two kinds of blood differ, however, within wide limits. 

 The following Table represents the average composition of the gases 

 obtained from an artery and a vein of the dog : 



From 100 vols. May b3 obtained 



Of arterial blood 

 Of venous blood 



Of oxygen Of carbon dioxide Of nitrogen 

 , 20 vols. . 40 vols. . 1 to 2 vols. 

 8 to 12 vols. . 46 . 

 Measured at 760 mm. and C. 



Barcroft has shown that the principle introduced by Haldane (v. p. 969) 

 for the determination of the oxygen combined in the form of oxyhaemoglobin 



FIG. 492. Barcroft's blood-gas apparatus. 

 A, for 1 c.c. ; B, for O'l c.c. blood. 



may be successfully applied to small quantities of blood, such as 1 c.c. or even 

 0-1 c.c., and that in the same sample of blood the carbon dioxide may be deter- 

 mined. In this way it becomes practicable to make blood-gas analyses in a 

 patient, or in experiments on small organs where it is desired to determine their 

 gaseous metabolism by comparing the arterial with the venous blood. The 

 apparatus for dealing with 1 c.c. of blood is shown in Fig. 492 A. 



The apparatus consists of two bottles of identical size (about 30 c.c.) attached 

 to a manometer, the tubing of which is 1 mm. bore. The manometer is filled 

 with clove oil of known specific gravity. To fill it take out the centre tube, 

 put in clove oil at A, put in the centre tube with the glass tube B open and some 

 pressure on the rubber tube c. The oil should stand about half way up each 

 tube; seal B in a flame. The following constants must be determined : (1) the 

 sectional area of the tubing A ; (2) the size of the bottles v. 



