270 THE INCOME OF ENERGY 



proportion to its oxygen capacity. The latter 

 can be easily and accurately determined by 

 means of the ferricyanide method. 1 Thus blood 

 of a certain oxygen capacity has also a certain 

 coloring power ; and it is possible to standardize 

 the coloring power in terms of the oxygen capa- 

 city. We can therefore make the unit of volume 

 the basis of our definition of the unit of color- 

 ing power employed in haemoglobin estimations. 

 Since, however, oxy-hsemoglobin is not stable, 

 I have adopted as a standard a dilute solution 

 of blood of known oxygen capacity saturated 

 with coal gas. 2 This solution is sealed up in 

 a narrow test-tube after all the contained air 

 has been displaced by coal gas, and when thus 

 completely sealed is permanent." 



The standard solution for the hsemoglobin- 

 ometer is a one per cent solution, saturated with 

 coal gas, of ox or sheep's blood of the average 

 oxygen capacity of the blood of normal adult 

 males, found to be 18.5 per cent. If it be borne 

 in mind that 100 per cent on the hsemoglobin- 

 ometer scale corresponds to an oxygen capacity 



1 In this method the oxygen is displaced from laked blood 

 by ferricyanide of potassium, and the resultant gas measured. 

 HALDANE : Journal of Physiology, 1900, xxv, pp. 295-302. 



2 Coal gas contains carbon monoxide as an impurity, and 

 thus converts the oxy-haemoglobin to CO-hsemoglobin. 



