REGULATION OF BREATHING 1? 
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 extremé 
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,+ 
or the equally onesided vitalism of the vitalistic 
minority. 
1As an example of these I may perhaps refer to Sir 
Edward Schafer’s Presidential address to the British Asso- 
ciation in 1911. 
