RESPIRATION 



273 



in proportions depending on their relative pressures and chemical 

 affinity. Carbon monoxide has an affinity about 150 times as great 

 as oxygen. Blood saturated with carbon monoxide, and diluted 

 1 in 200 times, has a pink colour; the extent of saturation with carbon 

 monoxide can be estimated by a method depending on the depth of 

 this colour. If three samples of blood (diluted 1 in 200) are taken, 

 and one is saturated with carbon monoxide (shaken with coal-gas), 

 the second partly saturated, and the third not at all, the colours of 

 the samples are obviously different. The normal sample is straw- 

 coloured. A standard solution of carmine can be run in from a pipette, 

 and the amounts found which will make Sample 2 and Sample 3 

 equal in pinkness to Sample 1 . From the relative amounts of carmine 

 used the degree of saturation of Sample 2 is discovered. 



FIG. 144. HALDANE'S APPARATUS FOR DETERMINING O 2 TENSION IN HUMAN 



BLOOD. 



R, T, C, Apparatus for br- athing air containing CO at measured concentration; 

 M, mouthpiece; V, valves made of pieces of intestine; B, air-bag for controlling 

 pressure during expiration ; G, meter. 



Now, when air containing 0-05 per cent, carbon monoxide is 

 breathed for a sufficient period to allow the whole blood to get into 

 equilibrium, the saturation with carbon monoxide is found to be less 

 than that when the blood is shaken with the same mixture outside 

 the body; particularly is this the case under conditions of oxygen 

 want e.g., at high altitudes, partial asphyxia when it is suggested 

 there would be secretion of oxygen into the blood by the lung. The 

 oxygen pressure in the arterial blood raised by secretion is supposed 

 to antagonize the union of carbon monoxide with the haemoglobin. 

 However, other explanations have been given of this result. The 

 technique of the method is as follows: 



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