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Hence the efficacy of skin inflictions in the discipline of sensitive beings.

Other things being the same, the sensibility of the skin to these two classes of feelings is greatest in parts most richly supplied with nerves, and where the discriminative or tactile sensibility is greatest, as in the tongue, the lips, and the palm

of the hand.

8. Other painful Sensations of the Skin.-Among these I would first advert to the sensation of tickling. On this Weber remarks, that the lips, the walls of the nasal openings, and the face generally, when touched with a feather, give the peculiar sensation of tickling, which continues till the part is rubbed by the hand. In the nose, the irritation leads at last to sneezing. The excitation extends to the ducts of the glands, which pour out their contents, and increase the irritation. The violent commotion produced by bodies in contact with the eye, is of the nature of tickling, accompanied by a flow from the glands, and readily passing into pain. Why some places are liable to this sensation, and others not, it is difficult to explain. The possession of delicate tactual discrimination is not necessary to the effect.

The singularity of tickling is the fact that a very trifling sensation prompts to extraordinary efforts of the will for deliverance. The tickling of the arm-pit, or the soles of a susceptible person, is as violently repudiated as the touch of a scalding surface.

There is one consideration that may help to account for the anomaly. It is the nature of tickling to stimulate intense reflex movements; these are, on their own account, a source of massive discomfort and repugnance. The same tactile feeling, if unaccompanied with reflex stimulation, might be wholly indifferent. This remark may apply to the tickling that precedes laughing and sneezing. The irritation of the fauces brings about, in the first instance, reflex contractions of the muscles of the throat; these are more or less acutely painful; thereupon, we give way to the farther impulse to spasmodic expiration.

Possibly the same explanation may be extended to the chafing and fretting of the skin, when too slight to be painful as a pungent smart. A reflex stimulus is applied when the nervous system is irritable, and when forced muscular movements would be painful and repugnant. It is not the sensation by itself that we dread, but the wakening up of activity when we are courting repose and quiescence.

All the parts of the skin are liable to yield painful sensations, especially under injury or distemper. The epidermis is itself insensible, but the true skin is extremely alive to feeling. When lacerated, chafed, or burnt, it causes acute pains. Its capillary vessels and numerous sweat glands and oil glands are, in all probability, the source of pleasurable or painful organic sensations. The long continued compression of the same part of the skin creates uneasiness. The hairs are themselves insensible, but by their attachment to the skin they are the media of sensation. The place of attachment of the nails is the seat of a violent form of acute pain, which has a facility of seizing on the imagination, and of exciting revulsion even in idea.

Clamminess is a distinct sensation arising from the adhesion of a substance to the skin, and is an uneasy feeling, the uneasiness being due to some interruption of the natural functions of the part.

9. (II.) Sensations of Temperature.-The feelings of heat and cold are most powerfully felt in the skin; the sensitiveness also extending to the gullet, the stomach, and the rectum. There is no reason for supposing that any other nerves than those of touch are needed to a rouse a sensation of warmth or of coolness. As to the mode of action, heat being a state of molecular motion will impart molecular disturbance to the nerves, and thus operate as a stimulant, favourably or unfavourably according to the circumstances.*

Sir William Hamilton thinks it probable that the sensation of heat depends on a peculiar set of nerves, for two reasons: 1st, Because certain sentient parts of the body are insensible to this feeling; and, 2nd, Because I have met with cases recorded, in which, while sensibility in general was

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The sensation of wetness seems to be nothing else than a form of cold.

As regards the discrimination of degrees of Temperature, it appears that we are equally sensitive at high and at low points of the thermometer. According to Weber, we can discriminate 14° Reaumur from 14.4°, as well as 30° from 30.4°; and the discrimination is all the better by the change being rapidly made. It is also better when the unequal temperatures are applied at the same time to contiguous. parts, than when the parts touched are remote from each other. The sensitiveness of different parts to temperature is not solely dependent on the abundance of nerves supplied to the part; some other circumstance at present unknown is in operation. Weber's graduated scale for heat is as follows:tip of the tongue, eyelids, lips, neck, trunk. In the face, breast, and abdomen, the central parts are less sensitive than the sides.

The sensitiveness is increased by extent of surface. In an experiment with dipping the finger into water at 32° R., and the whole hand in 291°, the latter appeared the warmer of the two.

It is remarked that when one part of the body touches another, the temperature being the same, the part endowed with the finer tactile power feels the other. If the temperaabolished, the sensibility to heat remained apparently undiminished.'— REID, p. 875.

On the other hand, the experiments of Weber, while leading to the conclusion that the integrity of the skin is necessary to the discrimination of degrees of temperature by touch, give no ground for supposing that any other nerve fibres than those of common tactile sensation are necessary.— CARPENTER'S Human Physiology, 4th edition, § 866.

Brown-Séquard is, however, of opinion that, in the spinal cord, the channel for conducting impressions of temperature is different from that for tactile impressions.

It may be remarked that the discriminative sensibility of the skin, shown in the feeling of plurality of impressions, implies an internal or central organization for receiving, independently, the stimuli of the different parts. Now, an internal derangement might vitiate this independent conveyance of impressions without destroying the sensibility of the fibres to the impulses of heat, or cold, or other strong irritation. It has been stated that when the thalami injured, tactile sensation is lost, but not the sensibility to pain.

optici are

tures are different, the first feels the second tactually, while the second feels the temperature of the first. The hand is not felt tactually by the brow, nor is the coldness of the brow felt by the hand.

It is a singular fact, discovered by Weber, in connexion with the sense of temperature, that when two substances of the same weight, but of different temperatures, are estimated by the sense of touch or of pressure, the colder appears the heavier. The depressing effect of the cold chill upon the mind may be the explanation. This is somewhat analogous to the perversion of our estimate of time by an unusual elation or depression of the general mental tone: in the one case we imagine it to pass rapidly, in the other slowly.

The feeling of temperature is an element in many discriminations, as in the distinction between stone and wood.

We pass now (III.) to the most intellectual sensations of Touch, and first to cases of Touch simply.

10. (1.) Impressions of distinguishable Points.-I have already called attention to the discriminative or articulate character of the sense of touch, whereby it receives distinguishable impressions from the variously situated parts of an extended surface. Very interesting differences in the degree of this discrimination are observable on different parts of the surface of the body, which have been especially illustrated by the experiments of Weber.

These consisted in placing the two points of a pair of compasses, blunted with sealing wax, at different distances asunder, and in various directions, upon different parts of the skin of an individual. It was then found, that the smallest distance at which the contact can be distinguished to be double, varies in different parts between the thirty-sixth of an inch and three inches; and this seems a happy criterion of the acuteness of the sense. We recognize a double impression on very sensible parts of the skin, though the points are very near each other; while, in parts of less acute sensibility, the impression is of a single point, although they may be, in reality, far asunder.

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'In many parts we perceive the distance and situation of two points more distinctly when placed transversely, than when placed longitudinally, and vice versa. For example, in the middle of the arm or fore-arm, points are separately felt at a distance of two inches, if placed crosswise; but scarcely so at the distance of three, if directed lengthwise to the limb.

'Two points, at a fixed distance apart, feel as if more widely separated when placed on a very sensitive part, than when touching a surface of blunter sensibility. This may be easily shown by drawing them over regions differently endowed; they will seem to open as they approach the parts acutely sensible, and vice versa.

'If contact be more forcibly made by one of the points than by the other, the feebler ceases to be distinguished; the stronger impression having a tendency to obscure the weaker, in proportion to its excess of intensity.

'Two points, at a fixed distance, are distinguished more clearly when brought into contact with surfaces varying in structure and use, than when applied to the same surface, as, for example, on the internal and external surface of the lips, or the front and back of the finger.

'Of the extremities, the least sensitive parts are the middle regions of the chief segments, as in the middle of the arm, fore-arm, thigh, and leg. The convexities of the joints are more sensible than the concavities.

'The hand and foot greatly excel the arm and leg, and the hand the foot. The palms and soles respectively excel the opposite surfaces, which last are even surpassed by the lower parts of the fore-arm and leg. On the palmar aspect of the hand, the acuteness of the sense corresponds very accurately with the development of the rows of papillæ; and where these papillæ are almost wanting, as opposite the flexions of the joints, it is feeble.

'The scalp has a blunter sensibility than any other part of the head, and the neck does not even equal the scalp. The skin of the face is more and more sensible as we