166 HEMOGLOBIN 



curve in a way which really expresses what the curve means. If 

 we plot along the ordinate the relative concentrations of oxy- to 

 carboxy haemoglobin, starting from zero and extending to infinity, 

 and plot along the abscissa the relative concentrations of oxygen 

 to carbon monoxide in the air to which the haemoglobin is 

 exposed also starting from zero, the curve given above would be 

 transformed as follows. Taking the points as numbered in Fig. 52, 

 1, 2, etc., we read: 



Serial number of point... 

 Percentage HbCO 

 Percentage CO in air ... 



Now to make the transformation we may select the first point, 

 23 per cent, of HbCO means 77 per cent, of HbOg, therefore the ratio 



HbO 77 



rruriA is H^ = 3-33. TMs is read along the ordinate (Fig. 53). The 



percentage of CO in air is -02, the ratio therefore of Og to CO is 



21 



-^ = 1050. This is plotted along the abscissa. The result is the 



point labelled 1 in Fig. 53, and so with the other points. We therefore 

 obtain the following data : 



This method of plotting has many advantages over that given 

 in Fig. 52. It enables the reader much more easily to imderstand 

 the real properties of the reaction. 



The first point to which attention may be drawn is that at which 

 the haemoglobin is half-oxy- and half-carboxyhaemoglobin, and at 



which the ratio .-tti pA-i = 1 (see point 4). At that point the rela- 

 tive concentrations of oxygen and CO in the air are ft^At = 310 : 1. 



The first thing to note then is that the carbon monoxide is 310 times 

 as strong as the oxygen, inasmuch as that in 1/310 of the concentration 

 it win grasp an equal quantity of haemoglobin. 



The next point is that whilst the quotient of the abscissa divided 

 by the ordinate (310 -r 1) naturally is 310, the quotient of the 



