90 THE NEW PHYSIOLOGY. 



might describe the structure and action of a machine. 

 But there is something which is almost totally lacking, 

 for there is no description of the organic regulation which 

 absolutely dominates all the mechanical and chemical 

 details. 



When, for instance, we examine the pumping move- 

 ments of the respiratory muscles, we find that they are 

 determined by what is required to maintain at a practi- 

 cally constant partial pressure the carbon dioxide and 

 oxygen in the arterial blood leaving the^ lungs. If the 

 carbon dioxide production and oxygen consumption are 

 increased ten times, the ventilation of the lungs will 

 also be increased nearly ten times, so as to prevent 

 more than a very slight increase in the carbon dioxide 

 pressure of the blood. If the carbon dioxide percentage 

 in the inspired air increases, there is a corresponding 

 result. If the oxygen pressure in the arterial blood 

 tends to fall, it is kept up partly by increased breathing 

 and partly by active secretion of oxygen inwards by the 

 lung epithelium. Failure in these regulative activities 

 produces urgent and dangerous symptoms. 



Here, therefore, we have constant, unmistakable, and 

 exact regulation of the quality of the arterial blood by 

 the breathing, and if we examine the structure of the 

 lungs and the nutritive process by which this structure 

 is maintained, the constant teleological regulation or 

 maintenance of structure is no less evident. Now the 

 very expression " teleological regulation " evokes at once 

 emphatic repudiation from most physiologists, as they 

 consider that it savours of mouldy metaphysics. Let 

 us, they argue, keep to facts capable of definite experi- 

 mental verification, and avoid all doubtful interpretations 



