The first faculty we behold in the living man, and that from which all his others flow, is feeling: however inexplicable this faculty may appear, on a first view, if it be examined closely, it will be found to be a consequence of the essence, or a result of the properties of organized beings; the same as gravity, magnetism, elasticity, electricity, &c. result from the essence or nature of some others. We shall also find these last phenomena are not less inexplicable than that of feeling. Nevertheless, if we wish to define to ourselves a clear and precise idea of it, we shall find that feeling is a particular manner of being moved—a mode of receiving an impulse peculiar to certain organs of animated bodies, which is occasioned by the presence of a material object that acts upon these organs, and transmit the impulse or shock to the brain.
Man only feels by the aid of nerves dispersed through his body; which is itself, to speak correctly, nothing more than a great nerve; or may be said to resemble a large tree, of which the branches experience the action of the root, communicated through the trunk. In man the nerves unite and lose themselves in the brain; that intestine is the true seat of feeling: like the spider in the centre of his web, it is quickly warned of all the changes that happen to the body, even at the extremities to which it sends its filaments and branches. Experience enables us to ascertain, that man ceases to feel in those parts of his body of which the communication with the brain is intercepted; he feels very little, or not at all, whenever this organ is itself deranged or affected in too lively a manner. A proof of this is afforded in the transactions of the Royal Academy of Sciences at Paris: they inform us of a man who had his scull taken off, in the room of which his brain was recovered with skin; in proportion as a pressure was made by the hand on his brain, the man fell into a kind of insensibility, which deprived him of all feeling. BARTOLIN says, the brain of a man is twice as big as that of an ox. This observation had been already made by ARISTOTLE. In the dead body of an idiot dissected by WILLIS, the brain was found smaller than ordinary: he says the greatest difference he found between the parts of the body of this idiot, and those of wiser men, was, that the plexus of the intercostal nerves, which is the mediator between the brain and the heart, was extremely small, accompanied by a less number of nerves than usual. According to WILLIS, the ape is, of all animals, that which has the largest brain, relatively to his size: he is also, after man, that which has the most intelligence: this is further confirmed, by the name he bears in the soil, to which he is indigenous, which is ourang outang, or the man beast. There is, therefore, every reason to believe that it is entirely in the brain, that consists the difference, that is found not only between man and beasts, but also between the man of wit, and the fool: between the thinking man, and he who is ignorant; between the man of sound understanding, and the madman: a multitude of experience, serves to prove, that those persons who are most accustomed to use their intellectual faculties, have their brain more extended than others: the same has been remarked of watermen, that they have arms much longer than other men.
However this may be, the sensibility of the brain, and all its parts, is a fact: if it be asked, whence comes this property? We shall reply, it is the result of an arrangement, of a combination, peculiar to the animal: it is thus that milk, bread, wine, change themselves in the substance of man, who is a sensible being: this insensible matter becomes sensible, in combining itself with a sensible whole. Some philosophers think that sensibility is a universal quality of matter: in this case, it would be useless to seek from whence this property is derived, as we know it by its effects. If this hypothesis be admitted, in like manner as two kinds of motion are distinguished in Nature, the one called live force, the other dead, or inert force, two sorts of sensibility will be distinguished, the one active or alive, the other inert or dead. Then to animalize a substance, is only to destroy the obstacles that prevent its being active or sensible. In fact, sensibility is either a quality which communicates itself like motion, and which is acquired by combination; or this sensibility is a property inherent in all matter: in both, or either case, an unextended being, without parts, such as the human soul is said to be, can neither be the cause of it nor submitted to its operation; but we may fairly conclude, that all the parts of Nature enjoy the capability to arrive at animation; the obstacle is only in the state, not in the quality. Life is the perfection of Nature: she has no parts which do not tend to it—which do not attain it by the same means. Life in an insect, a dog, a man, has no other difference, than that this act is more perfect, relatively to ourselves in proportion to the structure of the organs: if, therefore, it be asked, what is requisite to animate a body? we reply, it needs no foreign aid; it is sufficient that the power of Nature be joined to its organization.
The conformation, the arrangement, the texture, the delicacy of the organs, as well exterior as interior, which compose men and animals, render their parts extremely mobile, or make their machine susceptible of being moved with great facility. In a body, which is only a heap of fibres, a mass of nerves, contiguous one to the other, united in a common center, always ready to act; in a whole, composed of fluids and solids, of which the parts are in equilibrium, the smallest touching each other, are active in their motion, communicating reciprocally, alternately and in succession, the impression, oscillations, and shocks they receive; in such a composition, it is not surprising that the slightest impulse propagates itself with celerity; that the shocks excited in its remotest parts, make themselves quickly felt in the brain, whose delicate texture renders it susceptible of being itself very easily modified. Air, fire, water, agents the most inconstant, possessing the most rapid motion, circulate continually in the fibres, incessantly penetrate the nerves: without doubt these contribute to that incredible celerity with which the brain is acquainted with what passes at the extremities of the body.
Notwithstanding the great mobility with which man's organization renders him susceptible, although exterior as well as interior causes are continually acting upon him, he does not always feel in a distinct, in a decided manner, the impulse given to his senses: indeed, he does not feel it, until it has produced some change, or given some shock to his brain. Thus, although completely environed by air, he does not feel its action, until it is so modified, as to strike with a sufficient degree of force on his organs; to penetrate his skin, through which his brain is warned of its presence. Thus, during a profound and tranquil sleep, undisturbed by any dream, man ceases to feel. In short, notwithstanding the continued motion that agitates his frame, man does not appear to feel, when this motion acts in a convenient order; he does not perceive a state of health, but he discovers a state of grief or sickness; because, in the first, his brain does not receive too lively an impulse, whilst in the others, his nerves are contracted, shocked, and agitated, with violent, with disorderly motion: these communicating with his brain, give notice that some cause acts strongly upon them—impels them in a manner that bears no analogy with their natural habit: this constitutes, in him, that peculiar mode of existing which he calls grief.
On the other hand, it sometimes happens that exterior objects produce very considerable changes on his body, without his perceiving them at the moment. Often, in the heat of battle, the soldier perceives not that he is dangerously wounded, because, at the time, the rapidity, the multiplicity of impetuous motion that assails his brain, does not permit him to distinguish the particular change a part of his body has undergone by the wound. In short, when a great number of causes are simultaneously acting on him with too much vivacity, he sinks under their accumulated pressure,—he swoons—he loses his senses—he is deprived of feeling.
In general, feeling only obtains, when the brain can distinguish distinctly, the impressions made on the organs with which it has communication; it is the distinct shock, the decided modification man undergoes, that constitutes conscience. Doctor Clarke, says to this effect: "Conscience is the act of reflecting, by means of which I know that I think, and that my thoughts, or my actions belong to me, and not to another." From this it will appear, that feeling is a mode of being, a marked change, produced on our brain, occasioned by the impulse communicated to our organs, whether by interior or exterior agents, by which it is modified either in a durable or transient manner: it is not always requisite that man's organs should be moved by an exterior object, to enable him to feel that he should be conscious of the changes effected in him: he can feel them within himself by means of an interior impulse; his brain is then modified, or rather he renews within himself the anterior modifications. We are not to be astonished that the brain should be necessarily warned of the shocks, of the impediments, of the changes that may happen to so complicated a machine as the human body, in which, notwithstanding all the parts are contiguous to the brain, and concentrate themselves in this brain, and are by their essence in a continual state of action and re-action.
When a man experiences the pains of the gout, he is conscious of them; in other words, he feels interiorly, that it has produced very marked, very distinct changes in him, without his perceiving, that he has received an impulse from any exterior cause; nevertheless, if he will recur to the true source of these changes, he will find that they have been wholly produced by exterior agents: they have been the consequence, either of his temperament; of the organization received from his parents; of the aliments with which his frame has been nourished; besides a thousand trivial, inappreciable causes, which congregating themselves by degrees produce in him the gouty humour; the effect of which is to make him feel in an acute and very lively manner. The pain of the gout engenders in his brain an idea, so modifies it that it acquires the faculty of representing to itself, of reiterating as it were, this pain when even he shall be no longer tormented with the gout: his brain, by a series of motion interiorly excited, is again placed in a state analogous to that in which it was when he really experienced this pain: but if he had never felt it, he would never have been in a capacity to form to himself any just idea of its excruciating torments.
The visible organs of man's body, by the intervention of which his brain is modified, take the name of senses. The various modifications which his brain receives by the aid of these senses, assumes a variety of names. Sensation, perception, and idea, are terms that designate nothing more than the changes produced in this interior organ, in consequence of impressions made on the exterior organs by bodies acting on them: these changes considered by themselves, are called sensations; they adopt the term perception when the brain is warned of their presence; ideas is that state of them in which the brain is able to ascribe them to the objects by which they have been produced.
Every sensation, then, is nothing more than the shock given to the organs, every perception is this shock propagated to the brain; every idea is the image of the object to which the sensation and the perception is to be ascribed. From whence it will be seen, that if the senses be not moved, there can neither be sensations, perceptions, nor ideas: this will be proved to those, who can yet permit themselves to doubt so demonstrable and striking a truth.