THE GASES OF THE BLOOD 59 



bound to the alkalies of the serum (chiefly to the sodium 

 bicarbonate and, in smaller quantities, to the acid calcium 

 carbonate). As the whole blood contains more carbon 

 dioxide than the corresponding amount of plasma, the blood 

 corpuscles also contain this gas in an easily dissociated form, 

 perhaps united with the haemoglobin or the alkali phosphate. 



In a vacuum, the blood loses all the carbon dioxide not 

 only from the acid but also from the neutral carbonates, 

 because it contains substances of a weak acid character, 

 which drive the carbon dioxide out of its union with alkalies. 

 These substances are the proteids and the haemoglobin. 



The nitrogen of the blood is only physically dissolved. 

 The per cent of gases in the blood is : 



Arterial Blood. Venous Blood. 



Oxygen 19.2 vol. % 1 1.9 vol. % 



Carbon dioxide 39.5 " 45-3 " 



Nitrogen 2.7 " 2.7 " 



These volumes of the gases are measured at o C. and 760 mm 

 mercury pressure. The amount of oxygen in the arterial blood is 

 below that of saturation. By means of violent artificial respiration, 

 the amount of oxygen can be brought to 23$. The venous blood 

 is not half saturated with carbon dioxide. 



Arterial blood is bright red ; venous blood, dark red. 



The difference in color of arterial and venous blood is due to 

 the difference in oxygen present. Artificially we can change 

 arterial blood to dark red by taking away its oxygen (shaking with 

 gases free of oxygen), and venous to a bright red by shaking with 

 oxygen. 



When arterial blood becomes venous, the concentration and 

 alkalinity of the plasma are increased, for the following reasons : 

 The red blood corpuscles swell by the inhibition of water from the 

 plasma, leaving the plasma more concentrated. By the mass 

 action of the carbonic acid, hydrochloric acid is set free from the 

 sodium chloride; this hydrochloric acid enters the blood cor- 

 puscles, while the alkali carbonate remains behind. When blood 

 is rendered arterial, the opposite takes place. 



Venous blood is found in the veins (except pulmonary 

 veins), in the right heart and in the pulmonary artery; 



