The Essays of Adam Smith · Adam Smith
EXTERNAL SENSES;
Children, however, appear at so very early a period to know the distance, the shape, and magnitude of the different tangible objects which are presented to them, that I am disposed to believe that even they may have some instinctive perception of this kind; though possibly in a much weaker degree than the greater part {464} of other animals. A child that is scarcely a month old, stretches out its hands to feel any little plaything that is presented to it. It distinguishes its nurse, and the other people who are much about it, from strangers. It clings to the former, and turns away from the latter. Hold a small looking-glass before a child of not more than two or three months old, and it will stretch out its little arms behind the glass, in order to feel the child which it sees, and which it imagines is at the back of the glass. It is deceived, no doubt; but even this sort of deception sufficiently demonstrates that it has a tolerably distinct apprehension of the ordinary perspective of Vision, which it cannot well have learnt from observation and experience. Do any of our other senses, antecedently to such observation and experience, instinctively suggest to us some conception of the solid and resisting substances which excite their respective sensations, though these sensations bear no sort of resemblance to those substances?
The sense of Tasting certainly does not. Before we can feel the sensation, the solid and resisting substance which excites it must be pressed against the organs of Taste, and must consequently be perceived by them. Antecedently to observation and experience, therefore, the sense of Tasting can never be said instinctively to suggest some conception of that substance. It may, perhaps, be otherwise with the sense of Smelling. The young of all suckling animals, (of the Mammalia of Linnæus,) whether they are born with sight or without it, yet as soon as they come into the world apply to the nipple of the mother in order to suck. In doing this they are evidently directed by the Smell. The Smell appears either to excite the appetite for the proper food, or at least to direct the new-born animal to the place where that food is to be found. It may perhaps do both the one and the other.
That when the stomach is empty, the Smell of agreeable food excites and irritates the appetite, is what we all must have frequently experienced. But the stomach of every new-born animal is necessarily empty. While in the womb it is nourished, not by the mouth, but by the navel-string. Children have been born apparently in the most perfect health and vigour, and have applied to suck in the usual manner; but immediately, or soon after, have thrown up the milk, and in the course of a few hours have died vomiting and in convulsions. Upon opening their bodies it has been found that the intestinal tube or canal had never been opened or pierced in the whole extent of its length; but, like a sack, admitted of no passage beyond a particular place. It could not have been in any respect by the mouth, therefore, but altogether by the navel-string, that such children had been nourished and fed up to the degree of health and vigour in which they were born. Every animal, while in the womb, seems to draw its nourishment, more like a vegetable, from the root, than like an animal {465} from the mouth; and that nourishment seems to be conveyed to all the different parts of the body by tubes and canals in many respects different from those which afterwards perform the same function. As soon as it comes into the world, this new set of tubes and canals which the providential care of Nature had for a long time before been gradually preparing, is all at once and instantaneously opened. They are all empty, and they require to be filled. An uneasy sensation accompanies the one situation, and an agreeable one the other. The smell of the substance which is fitted for filling them, increases and irritates that uneasy sensation, and produces in the infant hunger, or the appetite for food.
But all the appetites which take their origin from a certain state of the body, seem to suggest the means of their own gratification; and, even long before experience, some anticipation or preconception of the pleasure which attends that gratification. In the appetite for sex, which frequently, I am disposed to believe almost always, comes a long time before the age of puberty, this is perfectly and distinctly evident. The appetite for food suggests to the new-born infant the operation of sucking, the only means by which it can possibly gratifying that appetite. It is continually sucking. It sucks whatever is presented to its mouth. It sucks even when there is nothing presented to its mouth, and some anticipation or preconception of the pleasure which it is to enjoy in sucking, seems to make it delight in putting its mouth into the shape and configuration by which it alone can enjoy that pleasure. There are other appetites in which the most unexperienced imagination produces a similar effect upon the organs which Nature has provided for their gratification.
The smell not only excites the appetite, but directs to the object which can alone gratify that appetite. But by suggesting the direction towards that object, the Smell must necessarily suggest some notion of distance and externality, which are necessarily involved in the idea of direction; in the idea of the line of motion by which the distance can best be overcome, and the mouth brought into contact with the unknown substance which is the object of the appetite. That the Smell should alone suggest any preconception of the shape or magnitude of the external body to which it directs, seems not very probable. The sensation of Smell seems to have no sort of affinity or correspondence with shape or magnitude; and whatever preconception the infant may have of these, (and it may very probably have some such preconception,) is likely to be suggested, not so much directly by the Smell, and indirectly by the appetite excited by that Smell; as by the principle which teaches the child to mould its mouth into the conformation and action of sucking, even before it reaches the object to which alone that conformation and action can be usefully applied. The Smell, however, as it suggests the direction by which the external {466} body must be approached, must suggest at least some vague idea or preconception of the existence of that body; of the thing to which it directs, though not perhaps of the precise shape and magnitude of that thing. The infant, too, feeling its mouth attracted and drawn as it were towards that external body, must conceive the Smell which thus draws and attracts it, as something belonging to or proceeding from that body, or what is afterwards denominated and obscurely understood to be as a sort of quality or attribute of that body.
The Smell, too, may very probably suggest some even tolerably distinct perception of the Taste of the food to which it directs. The respective objects of our different external senses seem, indeed, the greater part of them, to bear no sort of resemblance to one another. Colour bears no sort of resemblance to Solidity, nor to Heat, nor to Cold, nor to Sound, nor to Smell, nor to Taste. To this general rule, however, there seems to be one, and perhaps but one exception. The sensations of Smell and Taste seem evidently to bear some sort of resemblance to one another. Smell appears to have been given to us by Nature as the director of Taste. It announces, as it were, before trial, what is likely to be the Taste of the food which is set before us. Though perceived by a different organ, it seems in many cases to be but a weaker sensation nearly of the same kind with that of the Taste which that announces. It is very natural to suppose, therefore, that the Smell may suggest to the infant some tolerably distinct preconception of the Taste of the food which it announces, and may, even before experience, make its mouth, as we say, water for that food.
That numerous division of animals which Linnæus ranks under the class of _worms_, have, scarcely any of them, any head. They neither see nor hear, have neither eyes nor ears; but many of them have the power of self-motion, and appear to move about in search of their food. They can be directed in this search by no other sense than that of Smelling. The most accurate microscopical observations, however, have never been able to discover in such animals any distinct organ of Smell. They have a mouth and a stomach, but no nostrils. The organ of Taste, it is probable, has in them a sensibility of the same kind with that which the olfactory nerves have in more perfect animals. They may, as it were, taste at a distance, and be attracted to their food by an affection of the same organ by which they afterwards enjoy it; and Smell and Taste may in them be no otherwise distinguished than as weaker or stronger sensations derived from the same organ. The sensations of Heat and Cold, when excited by the pressure of some body either heated or cooled beyond the actual temperature of our own organs, cannot be said, antecedently to observation and experience, instinctively to suggest any conception of the solid and resisting substance which excites them. What was said of the sense of Taste may very properly be said here. Before we can feel those sensations, {467} the pressure of the external body which excites them must necessarily suggest, not only some conception, but the most distinct conviction of its own external and independent existence.
It may be otherwise, perhaps, when those sensations are either of them excited by the temperature of the external air. In a calm day when there is no wind, we scarcely perceive the external air as a solid body; and the sensations of Heat and Cold, it may be thought, are then felt merely as affections of our own body, without any reference to any thing external. Several cases, however, may be conceived, in which it must be allowed, I imagine, that those sensations, even when excited in this manner, must suggest some vague notion of some external thing or substance which excites them. A new-born animal, which had the power of self-motion, and which felt its body, either agreeably or disagreeably, more heated or more cooled on the one side than on the other, would, I imagine, instinctively and antecedently to all observation and experience, endeavour to move towards the side in which it felt the agreeable, and to withdraw from that in which it felt the disagreeable sensation. But the very desire of motion supposes some notion or preconception of externality; and the desire to move towards the side of the agreeable, or from that of the disagreeable sensation, supposes at least some vague notion of some external thing or place which is the cause of those respective sensations.
The degrees of Heat and Cold which are agreeable, it has been found from experience, are likewise healthful; and those which are disagreeable, unwholesome. The degree of their unwholesomeness, too, seems to be pretty much in proportion to that of their disagreeableness. If either of them is so disagreeable as to be painful, it is generally destructive; and, that, too, in a very short period of time. Those sensations appear to have been given us for the preservation of our own bodies. They necessarily excite the desire of changing our situation when it is unwholesome or destructive; and when it is healthy, they allow us, or rather they entice us, to remain in it. But the desire of changing our situation necessarily supposes some idea of externality; or of motion into a place different from that in which we actually are; and even the desire of remaining in the same place supposes some idea of at least the possibility of changing. Those sensations could not well have answered the intention of Nature, had they not thus instinctively suggested some vague notion of external existence.
Ideas discussed in this chapter
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