RESPIRATION 253 



is an "objective method," and therefore the only trustworthy one. 

 Hence, Barcroft argues, Hartridge's experiments, so far as they 

 go, furnish the only reliable evidence about oxygen secretion, as 

 to which they give a negative result. As a matter of fact there is 

 not a shadow of doubt that our method of testing the colorimetric 

 method was at least as exact as the final method used by Hartridge. 



Barcroft's reference to objective methods recalls to my mind 

 what happened when Hartridge came to Oxford to demonstrate 

 his method. It was apparently an "objective method," dependent, 

 like Hiifner's spectrophotometric method, on the exact positions 

 of absorption bands in the spectra of oxyhaemoglobin and CO 

 haemoglobin bands of which the "exact positions" can be quite 

 easily photographed. A solution of blood was prepared for dem- 

 onstration; and Hartridge, the late Professor Gotch, and I went 

 into a dark room and proceeded first to determine the zero point 

 on the scale of the apparatus. First one, and then the others of us 

 determined the zero point. But the results were all different, 

 though each one of us always got the same result. We stood there 

 in the dark, each suspecting the others of want of accuracy, but 

 afraid to say so. Suddenly the truth dawned on us. Even the 

 position of an absorption band is subjective ! 



And then, if our ears could have caught it, we might have 

 heard a gentle but kindly laugh. It came from a Spirit that flits 

 round old university walls and even wanders sometimes into 

 laboratories. It was the Spirit of Humanism that laughed, and it 

 always laughs when men find out with Socrates that what is ob- 

 jective is also subjective. 



Addendum.. Barcroft and his associates 39 have recently made a 

 very carefully planned attempt to see whether any evidence of oxy- 

 gen secretion could be obtained by analyses of the arterial blood. 

 Barcroft himself was the subject of the experiment, and he re- 

 mained for a week in a respiration chamber in which the oxygen 

 percentage was gradually lowered, until on the last day there was 

 only about 1 1 per cent of oxygen in the air, corresponding to an 

 altitude of 18,000 feet, or about 17,000 if allowance is made for 

 the presence in the air of about 0.5 per cent of CO 2 . There was 

 thus apparently every chance of acclimatization occurring. On the 

 other hand very little acclimatization seems to have actually oc- 

 curred, as the subject was very unwell, with slight rise of tempera- 



39 Barcroft, Cooke, Hartridge, T. and W. Parsons, Journ. of PhysioL, LIII, 

 p. 450, 1920. 



