CHAPTER III 



THE GASES OF THE BLOOD AND THE CHEMISTRY OF 

 RESPIRATION 



1. THE GASES OF THE BLOOD 



For the analysis of the gases of the blood, it is placed, at body 

 temperature, in a vessel from which the air has been removed by 

 a mercurial air-pump. The gases leave the blood, entering into 

 the vessel; they can then be collected and analyzed. 



The gases of the blood are oxygen, carbon dioxide, and 

 nitrogen. The oxygen is dissolved physically to only a very 

 small extent, the greater part being chemically united to the 

 haemoglobin, forming oxyh&moglobin. The oxygen must 

 be held chemically, as the quantity of the oxygen in the 

 blood is not proportional to the partial pressure * of the 

 oxygen upon the blood, as would be the case in a physical 

 solution. 



Oxyhaemoglobin is a compound easily undergoing dis- 

 sociation ; by its dissociation the oxygen is set free. 



The degree of dissociation of a compound, by which a gas is 

 set free, is dependent upon the temperature and the pressure of 

 the gas. In a vacuum and at the body temperature, oxyhaemo- 

 globin undergoes complete dissociation (not at o) ; in other 

 respects, the amount of haemoglobin chemically united with oxygen 

 increases with the partial pressure of the oxygen, but not propor- 

 tionally as in the mere physical solution. 



The carbon dioxide of the blood is also physically dis- 

 solved to but a small extent; most of it being chemically 



* In a mixture of gases the partial pressure of one of the gases is that part 

 of the whole pressure which the gas exerts by itself. 



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