Rate of reduction of haemoglobin 



39 



produce the reduction from 100 to 94 % at 18C., whilst BC repre- 

 sents the time necessary for the same reduction at 38 (J. ; the former 

 is 35 minutes the latter about 2'5 or at most 3 minutes. It is usual 

 to compare the rates at which chemical changes take place, not 

 over a range of 20 C. as in this case, but over a range of ten degrees. 

 If the times necessary to produce a given change at temperatures 

 20 C. apart be in the ratio 35 : 3, the corresponding ratio for a 

 difference of 10 C. will be the square root of the ratio of 35 : 3, 

 namely 3'4 : 1, i.e. the coefficient is increased between 3 and 4-fold 

 by a rise of temperature of 10 C. 



A few lines back I spoke of extrapolating the curve DEFG. Let 

 me say a word or two in justification of this phrase. I do not mean 



100 

 90 

 80 

 70 

 60 

 50 

 40 

 30 



20 



10 



20 



30 



40 



50 60 



70 



80 



90 



100 110 120 



FIG. 20. Curve representing the calculated degree of dissociation at any time in a 

 haemoglobin solution through which nitrogen bubbled at a uniform rate. Percentage 

 saturation plotted vertically, time in minutes horizontally. Points represent actual 

 determinations. 



merely producing the curve backwards by its general appearance, 

 though for the present purpose no practical error would be involved 

 by this procedure. I wish to make it clear that the line DEFG is a 

 definite curve with a definite equation. The reduction of haemoglobin 

 by nitrogen, if it takes place as a chemical breakdown, must obey laws 

 which prescribe a definite form to the curve relating the percentage 

 saturation to the time. The equation relating these two quantities 

 has been worked out by Hill, and DEFG as drawn in the figure is 

 such a curve. The coincidence of the points as determined experi- 

 mentally with the curve is sufficiently good. The test would however 

 have been more crucial had the points been more numerous. 



