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deeper source than the accidental effect of the deterioration of the material of the frame. The same changes which are wrought on the structure of the body in youth and in the spring of life, are going on in the last term of life; but the fabric is rebuilt on a different plan; each stage, from the embryo to the fœtus, the foetus to the child, from that to adolescence, to maturity, and to old age, has its outward form, as indicative of the season of life, but not of the perfection or imperfection of the gross material. We might as well consider the difference in the term of life of the annual or biennial plant as compared with the oak, or of the ephemeris fly as compared with the bird that hawks at it, to result from the qualities of the matter which form them, as that the outward characters of the different stages of human life, arise from the perfection or imperfection of the material of the body. Not only has every creature its appointed term of life, but parts of the body, in that respect, are independent of the whole; some organs, at their regulated period, shoot to perfection; and at their allotted time, decay, before the failure of the body. What can more distinctly show that so long as the processes of digestion and assimilation go on, the material of the frame is ever decaying, ever renewing, and never older, and never younger? We must conclude that the differences in outward appearances, at the distinct epochs of our life, have been designed as signs which the Creator intended should be interpreted; and that the tenure by which we hold life may be continually before us.
The grand phenomena of nature make powerful impressions on our imagination, and we acknowledge them to be under the guidance of Providence; but it is more pleasing, more agreeable to our self-importance, it gives us more confidence in that Providence, to discover that the minutest changes in nature are equally His care, and that "all things do homage." This exaltation of ourselves is not like the influence of pride or common ambition. We may use the words of Socrates to his scholar, who saw, in the contemplation of nature, only a proof of his own insignificance, and concluded "that the gods had no need of him;" which drew this answer from the sage: "The greater the munificence they have shown in the care of thee, so much the more honour and service thou owest them!"]
When the many beautiful fabrics built up within the animal
body are passed under review, and it is proved that they are not permanent, but are the product of an energy of life, which continues uniform in its operation, whilst all the materials upon which it works are changing-who can hesitate to believe, that the revolutions occurring in the inorganic world around us, are superintended by a presiding Power? The difficulty of comprehension here must be attributed to the partial view of these changes which we can alone obtain. Their fulfilment extends into periods far beyond our measure of time. Nevertheless, we cannot doubt that such a Power does overlook them; and we must acknowledge that a balance is preserved, and that order and harmony prevail.
OF SENSIBILITY AND TOUCH.
WE find every organ of sense, with the exception of that of touch, more perfect in brutes than in man. In the eagle, hawk, gazelle, and feline tribe, the perfection of the eye is admirable; in the dog, wolf, hyæna, as well as birds of prey, the sense of smell is inconceivably acute; and if we hesitate to assign a more exquisite sense of taste to the inferior animals, we cannot doubt their superiority in that of hearing. But in the sense of touch, seated in the hand, man claims the superiority; and it is of consequence to our conclusion that we should observe why it is so.
Some author has said that, accompanying the exercise of touch, there is a desire of obtaining knowledge; in other words, a determination of the will towards the organ of the sense. Bichat avers that touch is active, whilst the other senses are passive. This opinion implies something to be understoodsomething deeper than what is expressed. We shall arrive at the truth by considering that, in the use of the hand, a double sense is exercised. In touch, we must not only feel the contact of the object; but we must be sensible of the muscular effort made to reach or grasp it in the fingers. It is in the exercise of the latter power, that there is really any effort made. There can be no more direction of the will towards the proper nerve of touch, than there can be towards any sensible nerve. But, before entering on the consideration of the sensibility, and the actions, which belong to the fingers, we must attend to the common sense of feeling in the surface generally.*
Besides that common sensibility is bestowed upon the hand as upon other parts, and some inquiry into it is necessary for our subject, I enter upon its examination the more willingly,
* See the Account of the Author's | at the commencement of the volume. Discoveries in the Nervous System, -(S.)
because nothing can afford more surprising proofs of design and benevolence in the Author of our being, than this property. However obviously the illustrations which we have already given, from the mechanism of the body, point to the same conclusion, they are not comparable, in point of interest, to the examples which we are about to present, from the living endowments of the frame.
I have used the term common sensibility, in conformity with the language of authors and customary parlance; but the expressions, common nerves," and " common sensibility," in a philosophical inquiry, are inadmissible. Indeed, the use of these terms has been the cause of much of the obscurity which has hung over the subject of the nervous system; and of our blindness to the benevolent adaptation of the endowments of that system to the condition of animal existence. Thus it has been supposed that some nerves are but coarsely provided for sensation, while others, of a finer quality, are adapted to more delicate impressions. It has been assumed that the nerve of the eye is finer than the nerve of the finger-without considering that the retina* is insensible to qualities, of which the nerve of touch is cognisant. Nerves are, indeed, appropriated to peculiar senses, and to bestowing distinct functions; but delicacy of texture has nothing to do with that. It is not because the nerve of touch has a coarser or more common texture than the optic or auditory nerve, that it is insensible to light or to sound. The beauty and perfection of the system is, that each nerve is susceptible to its peculiar impression onl The nerve of the skin is alone capable of giving the sense of contact, as the nerve of the eye is alone capable of giving vision. If this appropriation resulted merely from delicacy of texture, if the retina were sensible to light only from possessing a finer sensibility than the nerve of touch, the acuteness of the sense would be a source of torment; whereas it is most beneficently provided that the retina shall not be sensible to pain, or be capable of conveying any impressions but those which operate according to its proper function, producing light and colour.
The pain experienced in the eye from irritation of dust, depends on a distinct nerve from that which bestows vision;
* The retina is the expansion of the optic nerve within the eye.
and again, the sensitive nerve of the eye is susceptible to a different kind of impression from the sensation of the body generally; of which more presently. When the surgeon performs the operation of couching for cataract, and the point of the needle passes through the outer coat of the eye, it gives the sensation of pricking, which is an exercise of the nerve of touch; but when the needle passes through the retina, which is the expanded nerve of vision, and forms the internal coat of the eye, it gives the idea of a spark of fire in the eye. The nerve of vision is as insensible to touch, as the nerve of touch is insensible to light.*
We form our notions of sensibility from that of the skin; it is in constant communication with things around us, and affected by their qualities; it affords us information which corrects the ideas received from the other organs of sense, and it excites our attention to preserve our bodies from injury. So familiar are we with the painful effects of injuries upon the surface, that all are apt to imagine that the deeper the injury, the more dreadful the pain. But that is not the fact; nor would it accord with the beneficent design which shines out everywhere. To such irritants as would give the skin pain, the internal parts are totally insensible. The sensibility of the skin not only serves to give the sense of touch to the surface, but it guards the parts beneath; and as the deeper structures cannot be reached except through the skin, and we must suffer pain in it before they can be injured, it would be superfluous to bestow sensibility upon the deeper parts themselves. If the internal organs possessed sensibility similar in kind and degree to that of the integument, so far from answering a useful purpose, it would have been, in the common exercise of the frame, a continual source of pain.
Surgeons, from becoming practically acquainted with a greater number of the phenomena on which physiology is founded than physicians, have perhaps superior opportunities of advancing that science. In performing an operation, the surgeon informs his patient, after he has cut through the skin, that the greatest pain is over; but if, in the advanced stage, he
*These views of the distinct functions of the nerves of sense, were published (1811) in the earliest state
ment of my observations on the Nervous System.