RELATION OF PHILOSOPHY TO PSYCHOLOGY. 
31 
APPLICATION TO PHILOSOPHY. 
I have dwelt on the adjustment of the boundaries of these 
two sciences, partly because it is in itself of great philosoph¬ 
ical interest but especially because a similar change is now 
going on and must continue to go on in our ideas of the 
relations of physiology to the science which deals with the 
distinctive phenomena of the human spirit, and which I 
have called philosophy. We have, I believe, drawn sharply 
the line of lower limit of physiology— i. e., its relation to chem¬ 
istry ; but where shall we draw the upper limit of physiology— 
i. e., its relation to philosophy ? The functions of plants and 
the so-called vegetal functions of animals— i. e., the nutritive 
and reproductive functions of these—of course, belong exclu¬ 
sively to physiology. But the distinctive animal functions, 
those connected with the nervous system, what shall we say 
of these? Nerve-functions include brain-functions—even 
the highest—viz., cerebral functions ; but indissolubly con¬ 
nected with cerebral functions are sensation, consciousness, 
volition. We cannot treat of nerve-functions without touch¬ 
ing these also; and yet these are included in all our works 
on mental philosophy. See again the steps of nerve-action 
in animals: (1) Impression on a nerve terminal; (2) Trans¬ 
mission along a sensory fiber; (3) Change in a central sen¬ 
sory cell; (4) Transmission by a connecting fiber to a central 
motor cell; (5) Change in a central motor cell; (6) Trans¬ 
mission along a motor fiber; (7) Muscular contraction, pro¬ 
ducing motion. Now, all this may take place reflexly and 
therefore without the slightest consciousness or will. Evi¬ 
dently in that case the whole series belongs to physiology 
alone. But sometimes— i. e., when the cerebrum is in¬ 
volved—there emerge from this series other phenomena, 
apparently of an entirely different order, viz., consciousness, 
sensation, will, emotions, desires, &c. Right here the line 
of separation used to be drawn and is still drawn by many, 
perhaps most, and philosophy becomes identified with psy¬ 
chology. All the changes in the reflex series given above 
