210 



Chapter XIII 



pump always broke down, especially so at low percentages of CO- 

 haemoglobin. He therefore discarded it in favour of another method 

 of calibration. Oxyhaemoglobin and carboxyhaemoglobin of equal 

 concentrations were placed in wedge-shaped troughs in apposition 

 (Fig. 101): by turning a screw these could be shifted perpendicularly 



100 



50 



eo. 



5O 100 



FIG. 103. The results given by spectroscope and gas pump compared. 

 Actual / CO vertical. Observed readings / CO horizontal. Pump o. Spectroscope . 



to the beam of light so that the light was always shining through oxy- 

 and carboxyhaemoglobin in known proportions to one another before 

 reaching the grating of the spectroscope. After the adoption of this 

 method complete harmony with the pump was obtained by Hartridge 

 ;and the subjective element to this extent removed. In the case of 



