REGULATION OF BREATHING 17 



to the delicacy of their mechanism, and not to the 

 interference of some mysterious guiding influence 

 such as the so-called "vital principle." 



But the vitalists can equally find confirmation in 

 the new facts. They can lay stress on the extreme 

 delicacy of the regulation, and the fact that in man 

 this delicate regulation is maintained, day after day, 

 and year after year, in spite of all kinds of changes 

 in the external environment, and in spite of the 

 metabolic changes constantly occurring in all living 

 tissues. These facts preclude the hypothesis that 

 the respiratory centre is a permanent structure so 

 stable that it is unaffected by changes in environment. 

 The regulation, if it be a mechanism, is utterly mys- 

 terious from the physical and chemical standpoint, 

 and necessitates the assumption that a special guiding 

 influence is present, such as does not exist, so far as 

 we know, in the inorganic world. The more delicate 

 and definite the physiological regulations which the 

 advance of experimental physiology is constantly dis- 

 covering, the stronger the case for vitalism. 



I have tried to put the case fairly on both sides ; 

 for both sides have always appealed to me strongly, 

 and I have been utterly unable to accept the one- 

 sided mechanistic arguments which have been put for- 

 ward by many leading physiologists in recent times, 1 

 or the equally onesided vitalism of the vitalistic 

 minority. 



1 As an example of these I may perhaps refer to Sir 

 Edward Schafer's Presidential address to the British Asso- 

 ciation in 1911. 



