CHAPTER IV.

THE SENSES.

"If it were possible for a human being to come into the world with a brain perfectly prepared to be the instrument of psychical operations, but with all the inlets to sensations closed, we have every reason to believe that the mind would remain dormant like a seed buried in the earth."-Dr. Carpenter.

"That the powers of the understanding would for ever continue dormant were it not for the action of things external on the bodily frame, is a proposition now universally admitted by philosophers.”—Dugald Stewart.

"Apprehension by the senses supplies directly or indirectly the material of all human knowledge, or at least the stimulus necessary to develop every inborn faculty of the mind."-Helmholtz.

"Even the highest ideas are slowly and gradually developed from the accumulation of sensual experience, and their truth is only guaranteed by the possibility of finding concrete examples for them in real existence."-Virchow.

"The activity of the mind is just as much the result of its consciousness of external impressions, by which its faculties are called into play, as the life of the body is dependent upon the appropriation of nutrient materials and the constant Influence of external forces."-Dr. Carpenter.

"As we perceive more accurately, so we remember more correctly, judge more soundly, and imagine more truly."-Dr. H. Maudsley.

HE senses are the means by which the mind obtains its knowledge of the external world. Shut out from all direct communication with the outer world, it knows, and can know, nothing of what exists or is passing there, but what comes to it through the senses.1 Its knowledge of what is external to itself is

1 "We perceive no external object but by means of certain bodily organs, which God has given us for that purpose."--Dr. Thos. Reid. "Our knowledge is limited to our sensibilities. We are able to know what things affect our various sensibilities, or what may be compounded of these, and our knowledge extends no farther "-Prof. Bain. "We may, for want of a better name, say with Condillac that the internal primordial event which constitutes our knowledge is sensation.”—M. Taine. "Knowledge is simply virtual feeling, the stored-up accumulations of previous experiences, our own and those of others."-G. H. Lewes,

therefore dependent upon the number, state, and condition of the sensory organs. A man with only one sense can know nothing of the external world but what is revealed to him through that one medium. If we suppose that sense to be sight, then the world will present itself to the mind only as it is seen,-no sound will ever issue from it, touch or feeling will give no information respecting it, it will yield no taste and no smell.1 In like manner, the individual who is destitute of one or more of the senses is entirely cut off from such kinds of knowledge as naturally come in through these. Thus the man who is born blind can form no conception of colour, nor can one congenitally deaf have any idea of musical tones.2 In every such case the man converses with the material world in utter ignorance of those properties of matter which can alone find entrance through these senses of which he is destitute.s

Even with all our senses there is every reason to believe that it is only a small portion of the outer world that is revealed to us by them, and that there exist around us, and contiguous to us, many objects that our present senses are unable to apprehend. An additional

1"We can conceive ourselves as endowed with smelling, and not enjoying any other faculty. In that case we should have no idea of objects as seeable, as hearable, as touchable, as tastable. Our life would be a train of smells, and nothing more.”—Jas. Mill.

2" When an individual is deprived of the organs of sight, no power of attention or continued effort of the will, or exercise of the other senses, can make him enjoy the class of sensations which is lost."-Sir C. Bell.

"The attentive study of cases in which there is congenital deficiency of one or more senses makes it evident that the mind is utterly incapable of forming any definite ideas in regard to those properties of objects of which these particular senses are adapted to take cognisance."-Dr. Carpenter.

"It does not seem at all improbable that there are properties of

sense might probably make revelations to us no less surprising than the sense of sight to one who has been born blind. Further, there are heights and depths in the phenomena of sense of which our present senses cannot take cognisance, but which would be apparent to them were they more acute or powerful. Certain of the lower animals have some at least of the senses in higher perfection than man, if they have not, as some think, senses of which he has no knowledge.2

Man, however, is able by means of instruments or appliances of different kinds to greatly extend the power of his senses. Thus by means of the microscope and matter of which none of our senses can take immediate cognisance, and which other beings might be formed to perceive in the same manner as we are sensible to light, sound, &c."-Dr. Carpenter. It may be that "within the field occupied by the visible and ponderable universe, there is existing and moving another element fraught with another species of life-corporeal, indeed, and various in its orders, but not open to the cognisance of those who are confined to the conditions of animal organisation. Is it to be thought that

the eye of man is the measure of the Creator's power?-and has He created nothing which He has not exposed to our senses? The contrary seems much more than barely possible; ought we not to think it almost certain ?"-Isaac Taylor.

"If a new sense or two were added to the present normal number in man, that which is now the phenomenal world for all of us might, for all we know, burst into something amazingly wider and different, in consequence of the additional revelations through these new senses."-Prof. Masson.

2" We find every organ of sense, with the exception of that of touch, more perfect in brutes than in man. In the eagle and the hawk, in the gazelle and in the feline tribe, the perfection of the eye is admirable; in the dog, wolf, hyæna, as well as in birds of prey, the sense of smelling is inconceivably acute; and if we should have some hesitation in assigning a more exquisite sense of taste to brutes, we cannot doubt the superiority of that of hearing in the inferior animals."-Sir C. Bell.

3 "All observing instruments, all weights, measures, scales, micro meters, verniers, microscopes, thermometers, barometers, &c., are artificial extensions of the senses; and all levers, screws, hammers, wedges, wheels, lathes, &c., are artificial extensions of the limbs.". H. Spencer.

telescope he is able to discern objects invisible to the naked eye; by means of measures and weights he can distinguish differences that are indistinguishable by the eye or hand; and by means of chemical tests he can determine the presence of substances that are indeterminable by taste or smell. These "supplementary senses," as they have been called, have done much to extend our knowledge of nature, and to reveal the presence of objects and forces that were before unknown.1

2

The senses, then, are certain organs of the body by means of which the mind acquires its knowledge of the external world, and of the properties of the various objects which it comprises. They are commonly reckoned five -sight, hearing, touch, taste, and smell; but physiologists generally add a sixth sense, the muscular, which reveals the state of the muscles, and thereby largely contributes to our knowledge of external objects. There are certain other feelings which are by some classed as sensations, having an organ or seat in the body, and consciously affecting the mind. Such are the feelings connected with the stomach or intestinal canal, as hunger, thirst, repletion, indigestion, &c., or such as arise from diseased or abnormal states of particular organs or tissues, as inflammation, cramp, burns, bruises, and the like. These are doubtless sources of

1 "When to the unaided senses science began to add supplementary senses in the shape of measuring instruments, men began to perceive various phenomena which eyes and fingers conld not distinguish. Of known forms of force minuter manifestations became appreciable, and forms of force before unknown were rendered cognisable and measurable."-H. Spencer.

2"The sensory organs are only instruments of the mind, which has its seat in the brain, and by means of nerves makes use of these instruments to obtain information of external objects.”—Prof. Bernstein.

"The complicated sensations in the intestinal canal... though obscure, and even unknown as individual sensations, often constitute

much pleasure or pain, and thus contribute largely to our mental experience, but they do little in the way of revealing to us the external world, or of adding to our knowledge of things around us. Their office is mainly

confined to making known the state and condition of the body itself in order to its maintenance in a sound and healthy condition.1

Each of the senses is so formed and constituted as to be susceptible to certain kinds of impressions made upon it from without, and which are conveyed by means of nerves to a central organ, where they become known to the mind. A sensation, then, is a mental impression produced by a material change effected by the action of an external object or stimulus on some part of the body which is sensitive to it, and conveyed to the brain. In other words, it is the mental representation of an external fact by which it is produced.2 Every normal sensation, therefore, involves: (1) an external agent or stimulus which impresses or acts upon the bodily organ; (2) a bodily organ which receives the impres

a general state of feeling which is sometimes exhilarating and sometimes depressing."-James Mill. "The massive influence of the systemic sensations in determining the desires, volitions, and conceptions of mankind, has not been adequately recognised. Yet everyone knows the effect of impure air or a congested liver in swaying the mental mood, and how a heavy meal interferes with muscular and mental exertion."-G. H. Lewes.

1 "The characteristic distinction between these common sensations and the sensations of the senses is that by the latter we gain knowledge of the occurrences and objects which belong to the external world, and that we refer the sensations which they produce to external objects, whilst by the former we only feel conditions of our own body."-Prof. J. Bernstein.

2 "A sensation is a mental representation, the internal sign of an external fact exciting it."-H. Taine. It is." the mental impression, feeling, or conscious state resulting from the action of external things on some part of the body called on that account sensitive".-Prof. Bain.