CH. X.] OXYHAEMOGLOBIN. 24! 



It forms compounds with oxygen and carbon mon- 

 oxide, called oxyhaemoglobin (Hb-O 2 ) and carboxyhae- 

 moglobin (Hb-CO). Both are dissociated into Hb and the 

 gas by exposure to a vacuum. Hb-CO is much more 

 stable than Hb-O 2 , and the avidity of Hb for CO is more 

 than 130 times greater than the avidity of Hb for O 2 . A 

 small percentage of CO in the air breathed will thus result 

 in the formation of relatively considerable amounts of 

 Hb-CO in the blood. This can be converted into Hb-O 2 

 by exposure to a high tension of O 2 , such as is obtained by 

 breathing pure O 2 . 



The Hb-O 2 obtained from certain animals crystallises 

 readily, but the crystals differ somewhat, according to the 

 animal from which they are obtained. Also the volume 

 of O 2 combining with i gram, of Hb varies, the figure for 

 the horse being i -34 cc. of O 2 per gram, of Hb. The oxygen 

 is probably united to the iron of the haematin molecule, 

 the reaction Fe + O 2 < > FeO 8 being the basis of the 

 reaction Hb + O 



^ u ,. volume of O 2 evolved in cc. . -, ,, 

 The ratio - - is called the 



weight of iron in grams. 



specific oxygen capacity. 



Theoretically it is 



O 2 _ i molecular volume O 2 _ 22,394 

 Fe i gram, molecule Fe 55*85 



401 



Recent analyses of the blood of various animals have 

 given the value 401-8 which agrees very closely with the 

 theoretical. 



The volume of oxygen loosely held by i gram, of 

 Hb-O 2 is i 345 cc. 



So the minimum molecular weight of ox3^haemo- 



globin is - = 16,712. 



1-345 



CALIFORNIA COLLEfli 



of PHARMACf . 



