RESPIRATION 413 



To calculate how much extra oxygen the blood will take up in simple 

 solution, we must know the partial pressure of oxygen at which the blood 

 taken from the living body is saturated, and this can be deduced pretty 

 accurately from the percentage saturation of the haemoglobin and the 

 dissociation curve of oxyhaemoglobin in human blood. Now it was found 

 by Meakins and Davies^^ that the haemoglobin of normal human arterial 

 blood is about 95 per cent saturated, which corresponds to an oxygen 

 pressure of 11 per cent of an atmosphere, or 84 mm. The coefficient of 

 absorption of oxygen in blood at 38° is .022. Hence there will be .24 cc. 

 of oxygen in simple solution in 100 cc. of arterial blood. At 15° the co- 

 efficient of absorption is .031 and at ordinary atmospheric pressures the 

 partial pressure of oxygen in the bottle will be 20.5 per cent of an 

 atmosphere. Hence .63 cc. of oxygen will be in solution in 100 cc. of 

 blood saturated with air at 15°, and the extra oxygen taken up in solu- 

 tion will be .39 cc. Thus the total extra gas taken up in solution will be 

 .42 + .39 = .81 cc. in 100 cc. of blood, and only the balance of the 

 proportion actually taken up in the blood flask will go to saturate the 

 haemoglobin. Hence if the temperature of the water bath is 15° the 

 allowance for gas in simple solution will be .81 cc. 



If the bath is above or below 15° this allowance will be a little less or 

 greater, and a calculation shows that for each degree above or below 15°, 

 between the temperatures of 20° and 10°, the allowance will have to be 

 diminished or increased by .038 cc. 



An example will make the calculation of the percentage saturation of 

 the haemoglobin clear. Let us suppose that 2.15 cc. of arterial blood have 

 been delivered into the flask and the constant reading of the burette 

 after temperature equilibrium had been obtained was .072 cc, and after 

 agitating the blood .030. Thus 0.042 cc. of gas had been absorbed from 

 2.15 cc. of blood, or 1.95 cc. from 100 cc. The temperature was 14° and 

 the barometer 755 mm. Hence the factor for reduction to dry gas at 0° 

 and 760 mm. was 0.930. Therefore the dry gas at standard pressure and 

 temperature was 1.81 cc. The temperature of the bath was 13°. Hence 

 .81 + .08 = .89 cc. went into physical solution, so that 0.92 cc. of oxygen 

 was absorbed by the haemoglobin. 



To determine the percentage saturation of the haemoglobin it is 

 necessary to know the total oxygen capacity of the haemoglobin ; and this 

 can now be determined directly. To the tube passing through the stopper 

 of the blood flask there is attached a loop of wire into which a small 

 tube of thin glass can be inserted. In the tube is placed .25 cc. of satu- 

 rated ferricyanide solution and the flask closed and reinserted in the 

 water bath till temperature equilibrium is reached. The burette is again 



"Meakins and Davies, Journ. of Pathol, and Bacter., XXIII, p. 451, 1920. 



