PHYSIOLOGY 
certain acts or motions has a powerful in- 
fluence in the animal economy. But it 
operates much more decidedly on the ani- 
mal, or exterior, than on the organic, or in- 
terior life. It has the effect of diminishing 
the sensibility of our organs, as appears from 
the effect of using pessaries in the vagina, 
catheters in the urethra, &c. Relative plea- 
sure or pain are brought by the influence of 
this principle to the state of indifference. 
Things are agreeable or disagreeable by a 
comparison between the impression they 
make on the senses and the state of mind 
receiving that impression. Hence the im- 
pressions produced on our organs in the 
cases just mentioned, although at first pain- 
ful, are soon disregarded. Pleasant sensa- 
tions are the same. The cook and the per- 
fumer are not alive to the enjoyments which 
they procure for others. The pleasing emo- 
tions connected with the sight and hearing 
are soon rendered obtuse by repetition ; and 
any pleasure constantly repeated produces 
the same series of feelings; uiz;. pleasure, 
indifference, satiety, and even aversion. 
The mind is the centre of these changes. 
It institutes a comparison between the ac- 
tual sensation and the preceding impres- 
sions, and in proportion to the difference 
between these will be the vivacity of the 
present impression. It belongs, therefore, 
to the nature of pleasure and pain to de- 
stroy themselves, and to cease to exist be- 
cause they have existed. The art of pro- 
longing the duration of our enjoyments con- 
sists in varying their sources. . 
Habit, however, which deadens sensation, 
augments and brings to perfection the 
judgment. 
Most of the functions of the organic life 
are removed from the dominion of habit ; 
viz. circulation, respiration, &c. ; yet the 
influence of this principle is unquestionable 
in some parts of the organic functions, as 
the urinary secretion, evacuation of feces, 
hunger and thirst, &c. 
Voluntary Motions and Muscular Action, 
Having already gone over the subject of 
sensation, one of the offices of the nerves, 
the other, motion, remains for considera- 
, tion. The motions of the 1)ody have been 
commonly divided into two classes, the vo- 
luntary and involuntary. The action of the 
heart, stomach, and intestines, &c. exem- 
plifies the latter; while the former are the 
actions of almost all the other muscles of 
the body. Some are of a doubtful nature, 
as those of respiration, of the ossicula audi- 
tus, and the cremasters. Different physio- 
logists assign these to one of the above 
classes, or to a mixed division. 
The arrangement is not unexceptionable. 
There are few functions feptirely free from 
the operation of the will, if we consider the 
connection of the imagination and passions 
of the mind with that power; as, on the 
contrary, many muscular motions, which 
were originally arbitrary, become by the 
force of habit quite involuntary. Thus we 
can hardly bend the little finger without 
the ring finger ; and cannot help winking if 
a person brings his finger rapidly towards 
our eye, although we are certain that he 
will not strike us. Again, muscles which 
usually obey the will, refuse obedience un- 
der certain circumstances ; hence the diffi- 
culty of describing a circle with the hand 
and foot of the same side in opposite direc- 
tions, of moving the two hands with an op- 
posite circular motion, &c. Numerous in- 
stances might be quoted of the power of the 
will over motions that are usually involun- 
tary; we shall merely mention the fact, 
supported by the personal testimonies of 
Drs. Barnard and Cheyne, of an English 
officer who could influence the action of 
his heart and arteries (“ Treat, on Nervous 
Diseases,” p. 307.) Perhaps these pheno- 
mena may be accounted for by a reaction 
of the sensorium, excited by a mental sti- 
mulus. 
We may observe of the voluntary motions 
in general, that they form the chief charac- 
ter that distinguishes the animal and vege- 
table kingdoms. No plant has yet been 
discovered that seeks its food by voluntary 
motion ; nor, on the contrary, is any animal 
known, that does not either possess a power 
of locomotion, or at least procure its food 
by the voluntary motion of some organ or 
member. 
These motions in our own bodies shew 
the very complete harmony between the 
mind and the material fabric, as we shall 
readily admit, when we observe the won- 
derful celerity with which the fingers of the 
violin player, or the organs of speech of a 
person speaking, move, and recollect that 
an act of volition is necessary for each 
motion. 
The distinguishing characteristic of mus- 
cular fibres is their irritability, the quality 
by which they contract in obedience to the 
will, or- on the application of stimuli. This 
is an endowment residing in all muscular 
organs, but not in equal degree. Tire hol- 
low muscles, which are subservient to the 
vited functions, bold the first rank; these 
