ORGANIC REGULATION 113 
mechanistic explanation implies the assumption of 
more and more definite and complex physical and 
chemical structure in the body, and the development 
and maintenance of this structure has then to be 
accounted for, with a resulting relapse into vitalism, 
whether acknowledged or only implied. The help- 
less struggling in this direction of the mechanistic 
school which still represents modern orthodox physiol- 
ogy will be a marvel to future generations. It is in 
vain that the mechanistic theorists endeavour to exor- 
cise what du Bois-Reymond called the “spectre of 
vitalism.” This spectre is nothing but the shadow 
‘ cast by the mechanistic theory itseli—a shadow which 
_has only become, and could only become, deeper the 
longer the mechanistic theory has lasted. 
Both the mechanistic and the vitalistic schools have 
survived up to the present day, but we can under- 
stand that actual investigators have preferred to avoid 
vitalism so far as they could, as the vitalistic hypothe- 
sis seemed to set a limit to experimental investigation, 
and they rightly and instinctively felt that there is no 
such limit. So long as vitalism seemed the only alter- 
native to mechanistic interpretations, they were driven 
towards the latter. In the din of controversy between 
vitalists and mechanists there was, however, a com- 
plete failure to go to the root of the matter, and en- 
quire into the validity of the assumptions as to physi- 
cal reality which were accepted by both sides. 
In considering the facts of physiology we have 
hitherto looked at them from the standpoint of the 
individual organism only. But we know that in all 
