PART II 



THE PASSAGE OF OXYGEN TO AND FROM THE BLOOD 



CHAPTER VI 



THE CALL FOR OXYGEN BY THE TISSUES 



THE classical work of Pfliiger (1) on the combustion of living 

 material settled for all time, it seems to me, the logical order in 

 which the constituent processes of respiration should be treated. 



The issue before Pfliiger may be stated in a few words. Is the 

 quantity of oxygen taken up by the cell conditioned primarily by the 

 needs of the cell, or by the supply of oxygen ? The answer was clear, 

 the cell takes what it needs and leaves the rest. Respiration there- 

 fore should be considered in the following sequence. Firstly the 

 call for oxygen, secondly the mechanism by which the call elicits a 

 response, the immediate response consisting in the carriage of oxygen 

 to the tissues by the blood and its transference from the blood to the 

 cell. Thirdly in the background you have the further mechanism by 

 which the blood acquires its oxygen. It is not the habit of writers 

 on respiration to adopt this order, quite the contrary, but their 

 reason for placing pulmonary respiration in the foreground of the 

 picture is a purely practical one pulmonary respiration is more 

 evident, both to the eye and to the understanding. I imagine they 

 will not quarrel with me if I make an attempt to treat the matter 

 in what appears to be its logical sequence and make some estimate 

 of the call which the blood has to meet, before entering into a dis- 

 cussion of how the call is to be met. 



The present chapter will deal with the following theme: "There 

 is no instance in which it can be proved that an organ increases its 

 activity, under physiological conditions, without also increasing its 

 demand for oxygen." 



The importance of the principle that increased activity of an 

 organ entails a call for oxygen has been self-evident ever since the 

 days of Ludwig. The reason why the work has not been carried out 

 on an extensive scale till recently is because the old methods were 

 quite inadequate. 



