BY

CHAPTER II.

OF SENSATION.

Y Sensations we understand the mental impressions, feelings, or states of consciousness resulting from the action of external things on some part of the body, called on that account sensitive. Such are the feelings caused by tastes, or smells, sounds, or sights. These are the influences external to the mental organization; they are distinguished from influences originating within, as, for example, spontaneous activity, the remembrance of the past, or the anticipation of the future.

The Sensations are classified according to the bodily organs concerned in their production; hence the division into five But along with distinctness of organ we have distinctness in the outward objects, and also in the inward consciousness. Thus objects of sight are different from objects of smell; or rather we should say, that the properties and the agency causing vision are different from the properties causing smell, taste, or hearing.

The difference of the mental feeling or consciousness in the various senses is strongly marked, being a more characteristic and generic difference than obtains among the sensations of any one sense. We never confound a feeling of sight with a feeling of sound, a touch with a smell. These effects have the highest degree of distinctness that human feelings can possess. The discrimination of them is sure and perfect.

We are commonly said to have five Senses, these being apparent to every observer: Sight by the eye, Hearing by the ear, Touch by the skin, Smell by the nose, Taste by the mouth. In addition to these, physiologists distinguish a sixth sense, of a more vague description, by the title of common or general sensibility, as will be seen in the following extract

from Messrs. Todd and Bowman.

Under the name of common or general sensibility may be included a variety of internal sensations, ministering for the most part to the organic functions and to the conservation of the body. Most parts of the frame have their several feelings of comfort and pleasure, of discomfort and pain. In many of the more deeply seated organs no strong sensation is ever excited, except in the form of pain, as a warning of an unnatural condition. The internal sensations of warmth and chillness, of hunger, thirst, and their opposites, of nausea, of repletion of the alimentary and genitourinary organs, and of the relief succeeding their evacuation, of the privation of air, &c., with the bodily feelings attending strongly excited passions and emotions, may be mentioned among the principal varieties of common sensation.'

In this enumeration we can see several distinct groups of feelings, and can refer them to distinct bodily organs. Hunger, thirst, their opposites, nausea, repletion, and evacuation of the alimentary tube, are all associated with the digestive system. They might therefore be termed the digestive sensations. The privation of air causes a feeling whose seat is the lungs, and is only one of many kinds of sensibility associated with respiration. The sensations of warmth and chillness connect themselves partly with the lungs and partly with the organic processes in general, more especially, perhaps, the circulation. and the various secretions. The genito-urinary organs have a class of feelings so very special and peculiar, that they had better not be included under common sensibility.

Looking at the very important classes of feelings here indicated, important at least as regards human happiness and misery, considering also that they are but a few examples chosen from a very wide field, it appears to me to be expedient to take them up in systematic detail, and for that purpose to provide a place for them among the Sensations. It is the business of a work like the present to review the entire range of human sensibility, in so far as this can be reduced to general or comprehensive heads; and the only question is, where ought these organic feelings to be brought in? I know of no better arrangement for them than to include them among the Sen

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sations. The only apparent objection is the want of outward objects corresponding to them in all cases. The feelings of comfort or discomfort arising from a circulation healthy or otherwise, are not sensations in the full meaning of the term; they have no distinct external causes like the pleasures of music, or the revulsion of a bitter taste. But the reply to this objection is, first, that in many cases, if not in all, an external object can be assigned as the stimulus of the feeling: for example, in all the digestive feelings, the contact of the food with the surface of the alimentary canal is the true cause or object of the feeling. In like manner, the respiratory feelings may be viewed as sensations having the air for their outward object or antecedent. And with reference to the cases where feeling cannot be associated with any external contact, as in the acute pains of diseased parts, what we may plead is the strong analogy in other respects between such feelings and proper sensations. In all else, except the existence of an outward stimulus, the identity is complete. The seat of the feeling is a sensitive mass, which can be affected by irritants external to it, and which yields nearly the same effects in the case of a purely internal stimulus. So much is this the fact, that we are constantly comparing our inward feelings to sensations; we talk of being oppressed, as with a heavy burden, of being cut, or torn, or crushed, or burned, under acute internal sensibility. Taking all these considerations together, I feel satisfied of the propriety of the common view which classes these feelings with sensations. In carrying out this conviction, I shall place them first in the order of the Senses, under the title of Organic feelings, or Sensations of Organic Life.

In the Senses as thus made up, it is useful to remark a division into two classes, according to their importance in the operations of the Intellect. If we examine the Sensations of Organic Life, Taste, and Smell, we shall find that as regards pleasure and pain, or in the Emotional point of view, they are of great consequence, but that they contribute very little of the permanent forms and imagery employed in our intellectual processes. This last function is mainly served by Touch, Hearing, and Sight, which may therefore be called the Intel

lectual Senses by pre-eminence. They are not, however, thereby prevented from serving the other function also, or from entering into the pleasures and pains of our emotional life.

SENSATIONS OF ORGANIC LIFE.

1. The classification of these is best made to proceed according to the parts where they have their seat We have already alluded to the organic feelings connected with one. tissue, the muscular; we ought now to notice the other tissues entering into the moving apparatus, namely, the Bones and Ligaments. The nerves and nerve centres are subject to feelings dependent on their growth and waste, and on the changes that they go through in health and disease. The Circulation of the Blood, with the accompanying processes of secretion, assimilation, and absorption, may be presumed to have a distinct range of sensibility. The feelings connected with Respiration are of a less ambiguous character than the foregoing. The sensations of Digestion are numerous and prominent.

2. I will pass over with very few remarks the Bones and Ligaments, whose sensibility would appear to be almost exclusively connected with injury or disease, appearing in that case under the form of acute pain, a form of sensibility that it will suffice to have dwelt upon once for all. The minute discrimination of forms of pain is highly serviceable to the physician, and, if susceptible of being accomplished with precision, would enter with propriety into a systematic delineation of the Human Mind; at present it will be sufficient to remark, that sensibility everywhere demands a distribution of nerve fibres, and that the bones and ligaments are supplied with these, and although not in great number, yet sufficient to agitate the nerve centres with overpowering intensity on particular occasions. The diseases and lacerations of the periosteum give birth to excessive pains. The ligaments are said to be insensible to the cut of a knife, while the feeling of their being wrenched is most acute and painful. In extreme fatigue, the ligaments and the tendons of the muscles would

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appear to act along with the muscular tissue in giving rise to the disagreeable feeling of the situation. The joints are noted on various occasions as the seat of pain. The diminution of atmospheric pressure consequent on ascending a great elevation causes an intense sensation of weariness in the hip joints. Fracture of the bones and laceration of the ligaments are among the most agonizing misfortunes of our precarious existence.

Organic Sensations of Nerve.

3. The nerves and nerve centres, apart from their action as the organs or medium of all human sensibility, have a class of feelings arising from the organic condition of their own tissue. Wounds and diseases of the nerves are productive of intense pains, witness tic douleureux and the neuralgic affections of the brain and spinal cord. Nervous exhaustion and fatigue produces a well known sensibility, very distressing in its extreme forms; and repose, refreshment, and stimulants engender an opposite condition through a change wrought on the substance of the nerve tissue.

The nervous pains arising from cuts, injuries, and disease of the substance are characterised by a most vehement intensity. It would appear that a conducting nerve fibre is never so powerfully agitated as when the irritation is directly applied to itself. When a muscle is spasmodically contracted, the influence passes from the muscular fibre to the nerve, and the affection of the nervous fibres is then only secondary; but in neuralgic affections the influence comes at first hand, and not by propagation from some other tissue. The pains of the nerves are of all degrees according to the irritating cause, but it is their nature to be more strongly felt than most other pains.

4. Nervous fatigue and exhaustion when carried beyond a certain pitch is an extremely trying condition. It is produced by excessive expenditure in one or other of the forms of nervous exercise; by emotions, by over-much thought, or by too long continued activity of either body or mind. The effect is doubtless to modify the nerve substance and its circulation,