OF THE SENSES IN GENERAL.
The animal body is composed of different matters, of which some are
insensible, as the bones, the fat, the blood, &c. and others, as the
membranes and the nerves, appear to be active substances, on which
depend the action of every member. The nerves are the immediate organs
of the mind, but which may be said to diversify from a difference in
disposition, insomuch, that according to their position, arrangement,
and quality, they transmit to the mind different kinds of sentiment,
which have been distinguished by the name of sensations, and which
appear, in effect, to have no resemblance to each other. Nevertheless,
if we consider that all external senses are only nervous membranes,
differently placed and disposed; that the nerves are the general
organs of feeling, and that in the animal body, no other substance is
possessed of this property, we shall be led to believe that the senses,
having all one common principle, and the nerves proceeding from the
same substance, though in various forms, the sensations which result
from them are not so essentially different as they at first appear.
The eye ought to be regarded as an expansion of the optic nerve,
whose position being more exterior than that of any other nerve, has
the most quick and the most delicate sensation. It will be moved,
therefore, by the smallest particles of matter, as those of light;
and will consequently give us sensations of distant bodies, provided
they produce or reflect those small particles. The ear is not placed
so exteriorly as the eye, and in which there not being so great an
expansion of nerves, will not be possessed of the like degree of
sensibility, nor will it be affected by particles more gross, as those
which form sounds, and will give us sensations of such distant objects
as can put those particles in motion. As they are much grosser than
those of light, and have less quickness, they cannot extend themselves
so far; and consequently the ear will not give us sensations of objects
so distant as those which the eye communicates. The membrane, which is
the seat of smell, being still less furnished with nerves than the ear,
it will only give us sensations of particles of matter which are more
gross and less remote, such as the odour from bodies, which may be said
to be the essential oils which exhale and float in the air, as light
bodies swim upon the water. As the nerves are also in less quantity,
and more divided over the tongue, and palate, and the odoriferous
parts are not strong enough to affect them, the oily or saline parts
must detach themselves from other bodies, and lodge upon the tongue
to produce the sensation of taste. This sense differs materially from
that of smelling, because the last brings to us sensations of things
at a certain distance, but the former requires a kind of contact, which
operates by the means of the fusion of certain parts of matter, such as
salts, oils, &c. In short, as the nerves are minutely divided, and as
the skin affords them but a very thin covering, no particles of matter
so small as those which form light, sound, or odours, can affect them;
and the sense of feeling gives us no sensation of distant objects, but
of those only whose contact is immediate.
It appears, therefore, that the difference between our senses is
occasioned by the more or less exterior position of the nerves, and of
their greater or smaller quantity in the different organs. It is for
this reason that a nerve, when irritated by a stroke, or uncovered by a
wound, gives us often the sensation of light, without the assistance,
of the eye; and from the same cause we often experience sensations of
sound, though the ear be not affected by any thing exterior.
When the particles of luminous or sonorous matters are re-united
in great quantities, they form a kind of solid body, that produces
different kinds of sensations, which appear not to have any relation
with the first. The particles which compose light being collected in
great quantities, affect not only the eyes but also the nervous parts
of the skin, and produce the sensation of heat, which is a sentiment,
different from the first, though originating from the same cause. Heat,
then, is a sensation arising from a contact with light, which acts as
a solid body, or as a mass of matter in motion. The action of light,
like other matters in motion, is evident when we expose, light bodies
to the focus of a burning glass; the action of the light communicates
before even it heats them, a motion by which they are disturbed and
displaced. Heat, then, acts as solid bodies act upon each other, since
it is capable of displacing light matters, and communicating to them a
movement of impulsion.
The like happens when the sonorous particles are collected in great
quantities; they produce sensible agitation, which is very different
from the action of sound upon the ear. Any violent explosion, as a loud
clap of thunder, shakes us, and communicates a kind of trembling to all
the neighbouring bodies. Sound then also acts as a solid body, for it
is not the agitation of the air which causes this tremulous motion,
since even at that time we do not remark that it is accompanied with
the wind; besides, however strong the wind may be, it never produces
such violent agitations. It is by this action of the sonorous particles
that a cord in vibration sets the next in motion; and we ourselves
feel, when the noise is violent, a kind of fluttering very different
from the sensation of sound by the ear, although it be an effect of the
same cause.
All the difference in our sensations are produced by the greater or
smaller number, and by the more or less exterior position of the
nerves, which is the cause that some of our senses, as the eye, ear,
and smell, may be affected by the small particles which exhale from
particular bodies; others, as tasting and feeling, require actual
contact, or more gross emanations, so as to form a solid mass; and it
is this feeling which gives us the sensation of solidity, or fluidity,
and of the heat of bodies.
A fluid differs from a solid, because it has not any particles gross
enough to admit us to grasp it on different sides at one time. The
particles which compose fluids cannot touch each other but at one
point, or so few points, that no part can have any considerable
adliesion with another. Solid bodies, reduced even into an impalpable
powder, do not absolutely lose their solidity, because the parts,
touching each other by many sides, preserve a degree of cohesion; and
this is the reason why we can make them up in masses, and squeeze them
together.
The sense of feeling is spread over the whole body, but employs itself
differently in different parts. The sensation which results from
feeling is excited by the contact of some foreign body to that of our
own. If we apply a foreign body against the breast or shoulder we
shall feel it, but without having a single idea of its form, because
the breast or shoulder touches but one side only. It is the same with
respect to all other parts which cannot bend themselves round or
embrace at one time many parts of foreign bodies. Those parts of our
body, which, like the hand, are divided into many flexible and moveable
parts, and can apply themselves at one time upon different sides of a
foreign body, are those only which can give us the ideas of their form
and size.
It is not, therefore, because there are a greater quantity of nervous
tufts at the extremity of the fingers than in any other part of the
body, that the hand is, in effect, the principal organ of feeling,
but merely because it is divided into many parts all moveable, all
flexible, all acting at the same time, and are all obedient to the
will; and which alone gives us distinct ideas of the figure and form
of bodies. Feeling is no more than a contact of superficies, and the
superficies of the hand are greater, in proportion, than that of any
other part of the human body, because there is not any one which is
so greatly divided. This advantage, when added to those derived from
the flexibility of the fingers, suffices to render this part the most
perfect organ to give us the exact and precise ideas of the form of
bodies, and, if the hand had twenty fingers, it is not to be doubted
but that the sense of feeling would be infinitely more perfect; and if
we should suppose that it were divided into an infinity of parts we
should have, even in the very moment of the touch, exact and precise
ideas of the figure and difference of bodies, however small. If, on
the contrary, the hand were without fingers, we should have but very
imperfect and confused knowledge of the objects which surround us.
Animals which have hands appear to be the most acute; apes do things
so resembling the mechanical actions of man that they seem to be
actuated by the same sensations; but those animals which are deprived
of hands having not any part divided and flexible enough to be able to
twist round the superficies of bodies, they cannot have any precise
notion either of the form or size of them. It is for this reason that
we often see them frightened at objects which they ought to be the best
acquainted with. The principal organ of their feeling is the muzzle,
because it is divided in two parts by the mouth, and because the tongue
serves them for touching bodies, and turning them, which they do over
and over again, before they take them between their teeth. It may also
be conjectured, that animals, which, as the scuttle-fish, the polypus,
and many insects, have a great number of arms or paws, which they can
unite and join, may also have an advantage over others, in knowing
how to chuse what is most agreeable to them. Fishes, therefore, whose
bodies are covered with scales, ought to be the most stupid of all
animals, for they cannot have any knowledge of the form of bodies; and
their sense of feeling must be very obtuse, since they cannot feel but
through the scales. Thus all animals, whose bodies have no divided
extremities, as arms, legs, paws, &c. will have much less sense of
feeling than others. Serpents, however, are less stupid than fishes,
because, although they have no extremities, and are covered with a hard
and scaly coat, they have the faculty of bending round foreign bodies,
and by that means obtaining some conception of their form and magnitude.
The two great obstacles to the exercise of the sense of feeling then
are, first, the uniformity of the figure of the body of the animal, or
the defect of the different divided and flexible parts; and secondly,
the cloathing of the skin, whether with hair, feathers, scales, shells,
&c. The more this cloathing is hard and solid, the less the sentiment
of feeling will be; and the finer and more delicate the skin, the
sense of feeling will be the more quick and exquisite. Women, among
other advantages over men, have their skin more fine, and the sense of
feeling more delicate.
The foetus in the womb of the mother, has a very delicate skin;
it must therefore feel every exterior impression in the most acute
manner; but as it swims in a liquid, and as liquids break the action
of all the causes which may occasion any shock, it can but very seldom
be injured, and never without some violent shock be received by the
mother. Although the sense of feeling depends, in a great measure upon
the fineness of the skin, yet, as it can have but little exercise in
the foetus state, so can it have but little sensation arising from
feeling.
In a new-born infant, the hands remain as useless as in the foetus,
because, by swaddling they are not permitted to make use of them, till
the end of six or seven weeks; by this absurd custom, we retard the
unfolding of this important sense on which all our knowledge depends;
and therefore we should act more wisely, were we to allow the infant
the free use of its hands the moment of its birth, as it would then
sooner acquire ideas of the form of things; and who knows how far
our first ideas have an influence over our subsequent ones? One man,
perhaps, possesses more ingenuity, or capacity than another, merely
because in his earliest infancy he was allowed to make a greater and
readier use of this sense. As soon as children are indulged with the
liberty of their hands, they endeavour to touch whatever is presented
to them. They take pleasure in handling every thing they are capable
of grasping; they seem as if desirous to find out the form of bodies,
by feeling them on every side; and they amuse or instruct themselves
in this manner with new objects. And which predilection for novelty
remains our favourite amusement through life.
It is by feeling alone that we can attain any complete and certain
intelligence, and it is by that alone, all the other senses are
prevented from being perpetual sources of illusion and error. But in
what manner is this important sense developed? In what manner are
our first ideas attained? Have we not forgot every thing that passed
during the cloud of infancy? How shall we trace our thoughts back to
their origin? Even in attempting thus to trace them, is there not
presumption? There is, and were the object in view of less importance,
with justice might it be stigmatized, but as the mind cannot be
employed in a more noble research, every effort may surely be exerted
in so important a contemplation.
Let us suppose, then, a man newly brought into existence, whose
body and organs were perfectly formed, but who, awaking amidst the
productions of Nature, is an utter stranger to himself and every thing
he perceives. Of a man thus circumstanced what would be the first
emotions, the first sensations, the first opinions? Were he himself
to give us a detail of his conceptions at this period, how would he
express them? Might it not be in some measure as follows? And here let
us suppose such a man to speak for himself.
"Well do I recollect that joyful, anxious moment, when I first became
conscious of my own existence; I knew not what I was, where I was,
nor from whence I came. On opening my eyes, what an addition to my
surprise! The light of day, the azure vault of heaven, the verdure of
the earth, the transparency of the waters, all employed, all animated
my spirits, and filled me with inexpressible delight.
"At first, I imagined that all those objects were within me, and
formed a part of myself. Impressed with this idea, I turned my eyes
toward the sun, whose splendour instantly dazzled and overpowered
me. Involuntarily I closed my eye-lids, though not without a slight
sensation of pain; and, during this short interval of darkness, I
imagined that I was about to sink into nothing.
"Full of affliction and astonishment at this great change, I was roused
by a variety of sounds. The whistling of the breezes, and the melody
of birds, formed a concert, of which the soft impression pervaded the
inmost recesses of my soul. I continued to listen, and was persuaded,
that this music was actually within me.
"So much was I engrossed with this new kind of existence, that I
entirely forgot the light part of my being, which I had known the
first, till again I opened my eyes. What joy to find myself once more
in possession of so many brilliant objects! The present pleasure
surpassed the former, and for a time suspended the charming effect of
sound.
"I turned my eyes upon a thousand different objects, I soon found that
I could lose and restore them at pleasure; and with a repetition of
this new power I continued to amuse myself.
"I began to see without emotion, and to hear without confusion, when
a light breeze, communicated a new sensation of pleasures by wafting
its perfumes to my nostrils, and excited in me a kind of additional
self-love.
"Occupied by these different sensations, and impelled by the various
pleasures of my new existence, I instantly arose, and was transported
by perceiving that I moved along, as if by some unknown, some hidden
power.
"Hardly had I advanced one step, when the novelty of my situation
rendered me immoveable. My surprise returned; for I supposed that all
the objects around me were in motion, and the whole creation seemed
once more to be in disorder.
"I carried my hand to my head, I touched my forehead, I felt my whole
frame. Then I found my hand to be the principal organ of my existence.
All its informations were so distinct, so perfect, and so superior to
what I had experienced from the other senses, that I employed myself
for some time in repeating its enjoyments. Every part of my body, which
I touched with my hand, seemed to touch my hand in turn, and actually
gave back sensation for sensation.
"It was not long before I perceived that this faculty of feeling was
expanded over my whole frame, and I began to discover the limits of
my existence, which at first I had supposed of an immense extent, and
diffused over all the objects I saw.
"Upon casting my eyes upon my body, I conceived it to be of a size
so enormous, that all other objects seemed to be, in comparison, as
so many luminous particles. I gazed upon my person with pleasure. I
examined the formation of my hand, and all its motions; and my hand
appeared to be more or less large, in proportion as it was more or less
distant from my eyes. On bringing it very near, it concealed, I found,
almost every other object from my sight.
"I began to suspect there was some fallacy in the sensation I
experienced from the eye, because as I perceived my hand was only a
small part, I could not conceive how it should appear so large; I
therefore resolved to depend for information upon the touch, which as
yet had never deceived me. This precaution was highly serviceable. I
renewed my motions, and walked with my face turned toward the heavens.
Happening to strike lightly against a palm-tree, I was dismayed, and
laid my hand, though not without fear, upon this object, and found it
to be a being distinct from myself, because it did not return double
sensation as my own body had done. Now it was that, for the first time,
I perceived there was something external, something which did not form
an actual part of my own existence.
"From this new discovery I concluded that I ought to form my opinion
with respect to external objects, in the same manner as I had done
with respect to the parts of my body. I resolved, therefore, to feel
whatever I saw, and vainly attempted to touch the sun, I stretched
forth my arm and found nothing but an airy vacuum. Every effort I
made, as each object appeared to me equally near, led me from one fit
of surprize into another, nor was it till after an infinite number
of trials that I was enabled to use the eye as a guide to the hand,
and that I perceived there were some objects more remote from me than
others.
"Amazed and mortified at the uncertainty of my state, and the endless
delusions to which I seemed subjected, the more I reflected the more
I was fatigued and oppressed with thought; I seated myself beneath
a tree loaded with delicious fruit, within my reach. On stretching
forth my arm, and gently touching it, the fruit instantly separated
from the branch; I seized it, and being able to grasp in my hand an
entire substance, which formed no part of myself, appeared of great
importance. When I held it up its weight, though in itself trivial,
seemed like an animated impulse, in conquering which I found another
and a greater pleasure.
"I held the fruit near my eye, and I considered its form and its
colours. Its fragrance prompted me to carry it near my lips, and with
eagerness did I inhale that fragrance. The perfume envited my sense of
tasting, which I found to be superior to that of smelling. What savour,
what novelty of sensation, did I now experience. Nothing could be
more exquisite. What before had been pleasure was how heightened into
luxury. The power of tasting gave me the idea of possession. I imagined
that the substance of this fruit had become a part of my own, and that
I was empowered to transform things without me at will.
"Charmed at the idea of this new power, and incited by the sensations I
had already experienced, I continued to pluck the fruit and to eat. At
length, however, an agreeable languor stealing upon my senses, my limbs
became heavy, and my soul seemed to lose its activity. My sensations,
no longer vivid and distinct, presented to me only feeble and irregular
images. In the instant, as it were, my eyes became useless, closed, and
my head, no longer borne up by the strength of the muscles, sunk back,
and found a support upon the verdant turf beneath me.
"To every thing around me I was now lost and insensible. Of my very
existence I retained not the smallest sensation. How long I continued
thus asleep I know not, for as yet I had not formed the smallest
idea of time. My awaking appeared like a second birth, and I only
felt that my existence had experienced a certain interruption. This
short annihilation produced in me a sensation of fear, and I began to
conclude that I was not to exist for ever.
"In this state of doubt and perplexity I also began to suspect that
sleep had robbed me of some part of my late powers, when turning
around, in order to resolve my doubts, with what astonishment did I
behold another form similar to my own? I took it for another self; and
I imagined that, far from having lost any thing during my late state of
annihilation, my existence was in reality doubled.
"Over this new being I carried my hand, and found, with rapture and
astonishment, that it was not a part of myself, but something more;
something more charming, something more glorious! nor could I help
supposing that my existence was about to be transfused entirely into
this, as it were, second part of my being. New ideas and new passions
now arose, took possession of my soul, and excited my curiosity. By the
touch of my hand I found her to be animated; expression and vivacity
darted from her eyes and impressed my soul, and love served to complete
that happiness which was begun in the individual, and every sense was
gratified in its full variety."