14 THE NEW PHYSIOLOGY. 



pressure of carbon dioxide in the alveolar air, and pre- 

 sumably, therefore, in the arterial blood, constant. In 

 reality, therefore, the lung ventilation is regulated in 

 accordance with the requirements of respiratory ex- 

 change ; and what seems to be true physiological 

 explanation has been advanced a short stage. 



The advance of knowledge with regard to the circu- 

 lation might be made the text of a similar discourse. 

 By a process of abstraction the circulation of the blood 

 may be regarded as a mere mechanical process, con- 

 nected only by the accidents of physical structure with 

 other physiological processes. Under the influence of 

 mechanistic theories the blood-pressure and rate of 

 blood-flow through different organs were indeed for long 

 supposed to be the primary determining cause of the 

 physiological activities of these organs, just as the rate 

 and depth of breathing were supposed to determine 

 the consumption of oxygen by the body. Evidence 

 is, however, accumulating on all hands, that the blood- 

 supply to various parts, like the air-supply to the lungs, 

 is in reality determined by physiological requirements. 

 In other words, it is a direct expression of the nature of 

 the organism, just as the common-sense idea of life 

 would lead us to expect. 



I may pass next to a branch of physiological know- 

 ledge which is still in its early infancy. Under the in- 

 fluence of mechanistic ideas physiology has for long 

 left completely out of account investigation into the 

 formation and maintenance of organic structure. For 

 mechanistic explanations structure had to be assumed, 

 and as a consequence anatomy was left high and dry in 

 a position of helpless isolation. If, however, the real 



