QUANTITY AND COMPOSITION OF BLOOD 



969 



THE OXYGEN CAPACITY OF THE BLOOD 



Instead of determining the haemoglobin we may measure directly 

 the oxygen capacity of the blood, since the oxygen-binding power of 

 this fluid is entirely dependent on the amount of haemoglobin it 

 contains. For this purpose we may make use of the fact discovered 

 by Haldane, that the combined oxygen in oxyhaemoglobin is liberated 

 rapidly and completely on addition of a solution of potassium ferri- 

 cyanide to laked blood, and may thus be easily measured with the help 

 of an apparatus similar to that used for determining urea in urine by the 

 hypobromite method. 



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FIG. 366. 



Haldane's method for determining the oxygen capacity 

 of the blood. 



The following description of the method is given by Haldane : 

 " Twenty cubic centimetres of the oxalated or defibrinated blood, thoroughly 

 saturated with air by swinging it round in a large flask, are measured out from a 

 pipette into the bottle A, which has a capacity of about 120 c.c. As it is important 

 to avoid blowing expired air into the bottle the last drops of blood are expelled 

 from the pipette by closing the top and warming the bulb with the hand. " Thirty 

 cubic centimetres are then added of a solution prepared by diluting ordinary strong 

 ammonia solution (sp. gr. 0-88) with distilled water to 5-577. The ammonia pre- 

 vents carbonic acid from coming off, while the distilled water lakes the corpuscles. 

 The blood and ammonia solution are thoroughly mixed by shaking, and at the end 

 of this operation the solution should appear perfectly transparent when tilted up 

 against the sides of the bottle.* About 4 c.c. of a saturated solution of potassium 



* If the solution were not transparent this would indicate that the laking 

 was incomplete, and more ammonia solution would need to be added. 



