573 
its source in the want of appropriate words (greater in Whytt’s time 
than now) to express the effect of physical agents on organic tissues. 
That there has always prevailed in physiology a tendency to express 
in a term not merely the property, but the cause of that property, 
which is exemplified in the contrast between the nearly synonymous 
words contractility and irritability, — the former signifying nothing 
more than the susceptibility of contraction, while the latter, the 
older word, bears reference to the cause of that susceptibility. That 
the idea attached by Whytt to “ sentient principle,” while he denies 
that it involves consciousness, may be gathered by some considera- 
tion of what dwelt in G-lisson’s mind, when, speaking of the obvious 
effect of impressions on the spinal cord in animals after decapitation, 
he says the cord perceives without sensation. 
The Memoir referring to the contrast between the effect of a drop 
of boiling water suddenly falling on the naked foot, and the effect 
of the sight of a drop of boiling water about to fall on the naked 
foot, points out that in the latter case the foot is moved by an intel- 
ligible force, namely, a volition, but in the former case, by a latent 
force, which is what Whytt calls his sentient principle. Further, 
if it be said, why introduce any force, sentient or not sentient, where 
nothing is by any research discoverable, that Whytt felt himself 
obliged by the usage of his age to invent an hypothesis, that some 
force might seem to intervene between the impression on the afferent 
nerve and the motor power imparted to the efferent nerve ; and 
that if he had felt himself at liberty to omit this hypothesis, his 
view would have been in general terms exactly that of the present 
day, — namely, that impressions made on the peripheral extremities 
of afferent nerves are reflected through the nervous centre into 
motor influence, transferable by efferent nerves to contractile organs. 
Again, that the modern view does not reject the idea of a force in- 
tervening between the impressions and the reflected motor influence, 
but merely omits all mention of it, because the connection between 
the impression and the subsequent motion is not spoken of in relation 
to cause and effect, but merely as the observed law of an ante- 
cedent and consequent, whence that Whytt’s mode of thinking does 
not in general terms differ from the modern view, except that he 
attempted to solve a difficulty which the modern view declines to 
meddle with. 
The Memoir, however, affords another reason why Whvtt felt 
