182 RESPONSE [IN THE LIVING AND NON-LIVING 
animal tissues, must necessarily be irresponsive, or 
incapable of being excited by stimulus—an assumption 
which has been shown to be gratuitous. 
This ‘unexplained conception of irritability became 
the starting-point, to quote the words of Verworn,! ‘ of 
vitalism, which in its most complete form asserted a 
dualism of living and lifeless Nature. . . . The vitalists 
soon,’ as he goes on to say, ‘ laid aside, more or less com- 
pletely, mechanical and chemical explanations of vital 
phenomena, and introduced, as an explanatory principle, 
an all-controllmg unknown and inscrutable “ force hyper- 
mécanique.” While chemical and physical forces are 
responsible for all phenomena in lifeless bodies, in 
living organisms this special force induces and rules all 
vital actions. 
‘Later vitalists, however, attempted no analysis of 
vital force; they employed it in a wholly mystical form 
as a convenient explanation of all sorts of vital phe- 
nomena. . . . In place of a real explanation a simple 
phrase such as “vital force” was satisfactory, and 
signified a mystical force belonging to organisms only. 
Thus it was easy to “explain” the most complex vital 
phenomena.’ 
From this position, with its assumption of the super- 
physical character of response, it is clear that on the 
discovery of similar effects amongst organic substances, 
the necessity of theoretically maintaining such dualism 
in Nature must immediately fall to the ground. 
In the previous chapters I have shown that not the 
fact of response alone, but all those modifications in 
’ Verworn, General Physiology, p. 18. 
