The acquisition of oxygen by the blood in the lung 211 



the pump the oxygen and CO were pumped from blood boiled in 

 vacuo in the presence of an alkaline solution of potassium ferri- 

 cyanide. The CO in the gas obtained was estimated by combustion 

 with a glowing platinum wire. 



The accompanying figures (102 and 103) will give the reader an 

 idea of the accuracy obtained by Hartridge. The first shows the 

 relation between the linear movement of the band and the percentage 

 of CO-haemoglobin, the latter being the ordinate and the former the 

 abscissa. The important point at the moment is the coincidence of 

 the individual observations with the line representing their mean. 

 In Fig. 103 is shown the correspondence (1) with the pump, and 

 (2) with the spectrometer (calibrated with the wedges) of samples of 

 blood containing known proportions of O.,- and CO-haemoglobin. 

 There are no published comparisons between the carmine method 

 and the pump and so far as I know none have ever been made. In 

 this way Hartridge checked his subjective method by an objective 

 one. 



By another method Hartridge has endeavoured, and with success, 

 to define the subjective element in his method. Two persons in- 

 specting the same solution of O 2 - and CO-haemoglobin will obtain 

 different readings with the instrument, i.e. they will place the index 

 at different places on the scale because their eyes see differently. 

 This of course is the demonstration of the subjective element. 



The carmine method and the spectroscopic one are alike in this 

 respect : there is no presumption that any two people see the same 

 tint when they look at a mixture of blood and carmine. In the case 

 of Hartridge's (5) method the subjective element is demonstrable in 

 units, and tests can therefore be instituted for the purpose of as- 

 certaining the degree to which the subjective element vitiates the 

 accuracy of the method. Winfield, whose eye differed considerably 

 from that of Hartridge, carried out control observations. He calibrated 

 the instrument which Hartridge had in use. The calibration was 

 made as in Hartridge's case with the wedge-troughs of oxy- and 

 CO-haemoglobin and gave the curve which is shown in Fig. 104. 

 This curve was roughly speaking parallel to Hartridge's curve. They 

 then independently made observations upon various samples of blood 

 containing O 2 - and CO-haemoglobin in unknown proportions, and each 

 interpreting his readings by his own curve arrived at identical 

 results. 



Lastly the method is susceptible of treatment in the way in which 



142 



