I. — PHYSIOLOGY, 165 



(I) Tlial. the liydiogcii ion couceniratioii ul' tliu blood rises ami 

 the total ventilation increases. On what hnes are you to 

 discuss whether the increased ventilation is due to 

 ' acidosis,' by which is meant in this connection the increased 

 hydrogen ion concentration of the blood, or to ' anoxaemia ' ';' 

 Clearly not on the lines that it must be due to one or other. 



In the above instance anoxaemia and acidosis are to some extent 

 dependant variables. I have chosen the above case because measure- 

 ments have been made throughout which make the various assump- 

 tions fairly certain, and tell us pretty clearly in what sort of chain 

 to string up the events, what is cause and what is effect. Clearly 

 it would be ridiculous to start a discussion as to whether the breath- 

 lessness was due to ' acidosis ' or ' anoxaemia.' Each has its place 

 in the chain of events. But I have heard discussions of whether other 

 phenomena of a more obscure nature were due to oxygen want or to 

 acidosis. Such discussions tend to no useful end. 



Nor is this the only problem with regard to oxygen want concerning 

 which my warning is needed. Oxygen want may act immediately in 

 at least two ways : 



(1) In virtue of absence of oxygen some oxidation which otherwise 



might take place does not do so, and thei'efore something 

 which might otherwise happen may not happen. For 

 instance, it naay be conceived that the respiratory centre can 

 only go througla the rhythmic changes of its activity as the 

 result of the oxidation of its own substance. 



(2) A deficient supply of oxygen may produce, not the negation 



of a chemical action, but an altered chemical action which 

 in its turn produces toxic products that have a secondary 

 effect on such an organism as the respiratory centre. 



Now these effects are not mutually exclusive. In the same category 

 are many arguments about whether accumulations of carbonic acid 

 act specifically as such or merely produce an effect in virtue of their 

 effect on the hydrogen ion concentration.. Here again the two points 

 of view are not, strictly speaking, alternatives, and, in some cases at 

 all events, both actions seem to go on at the same time. 



It will be evident that in any balanced action in which CO, is 

 produced its accumulation will tend to slow the reaction ; but, on the 

 other hand, the same accumulation may very likely raise the hydrogen 

 ion concentration, and in that way produce an effect. 



The relation of oxygen to haemoglobin seems to furnish a case in 

 point. Carbonic acid is known to reduce the affinity of hfemoglobin 

 tor oxygen, and other acids do the same. On analogy, therefoi'e, it 

 might have, and has, been plausibly argued that CO2 acts in virtue of the 

 change in reaction which it produces. Put into mathematical language, 

 tbe relation of the percentage saturation of oxygen to the oxygen 

 pressure of the gas dissolved in the haemoglobin solution is expressed 

 by the equation 



y Kx" a;" , .^ 1 



100 = i + K^ = L + of ' ''^'''' ^' = K' 



