CHAPTER XI 



THE RATE OF EXCHANGE OF OXYGEN BETWEEN THE 

 BLOOD AND THE TISSUES 



AT the risk of being thought to have taken somewhat of a jump 

 I shall discuss a very different aspect of the capillary circulation. 



At the end of Chapter V, I gave a short summary of the effect of 

 salts, temperature and carbonic acid upon the form of the dissociation 

 curve especially in relation to its physiological significance. I showed 

 that the form of the curve was such as to give it a double aspect ; to 

 favour both oxidation of the blood in the lungs and reduction of 

 the blood in the tissues. 



Whilst this is true it must be borne in mind that the dissociation 

 curve is essentially an equilibrium curve. One cannot tell from it, 

 how long will suffice for the oxidation of blood under any one set 

 of circumstances as compared with the time necessary to reduce it 

 under any other. 



But the conditions of respiration are not statical ones ; in no 

 tissue is there equilibrium between the tissue and the blood run- 

 ning through it ; therefore useful as is the knowledge which has been 

 acquired from a study of the effects of salts, temperature and acids 

 on the final equilibrium between haemoglobin and oxygen, the reader 

 cannot have any complete view of the significance of these factors 

 without some knowledge of the way in which they affect the rates of 

 oxidation and of reduction of the haemoglobin. 



I will therefore give some account of the experiments which have 

 been performed for the purpose of gaining such knowledge. 



The theory of the experimental procedure was very simple and was 

 an expansion of that which Hill and I used in studying the rate of 

 reduction of haemoglobin and which Mathison improved. It was to 

 pass a uniform stream of nitrogen through blood and to observe after 

 successive intervals of time the degree of reduction which had taken 

 place. 



