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Not only has the will no active share, except a restraining one, in the movements of tickling, but there are reasons for believing that tickling may be carried on in the total absence of both brain and head. It is certainly the case with frogs. A headless frog (and frogs will live, if well fed, for a long time without their heads) is quite as ticklish, or rather is far more ticklish, than one with his head on. If you pinch his foot, he will kick his leg out; if you prick his side, his arm will try to push the needle away. But it is not necessary to make cruel experiments on frogs to ascertain the truth of these statements; the same thing is sometimes shown in man, when virtually, though not actually, without a head. It not unfrequently happens that through violence or disease a man's spinal cord is separated from his brain. In such a case, the poor man's nervous system is divided into two parts. For instance, if he has tumbled down, and broken his back high up, say just below his neck, there will be his brain, with a number of nerves belonging to it, and a small portion of the spinal cord, all situated above the spot where the spinal column is broken, and below that spot there will be the rest of the spinal cord with all the nerves belonging to it. And between these two parts there will be no communication. The brain will have no power to move the legs ; the legs will have no means of telling the brain how they are and what they are doing. The man (that is to say, the brain or head) will be said to be completely paralyzed, being able neither to feel nor to move any part of his body that is situated below the point where the back is broken. If, in such a case as this, the soles of the feet be tickled, the legs will be drawn up or kicked out, very much as they would if the man were quite whole. But no part of the body above the seat of injury shares in this movement. On the contrary, the man himself does not even know what is going on unless he happens to see his legs move, and then he says that they move of themselves. It is quite possible, then, for tickling to take place without the brain having anything whatever to do with it.
What are the parts, then, that are necessarily concerned in tickling ? and how is the whole process carried out ? We may explain the matter in some such way as this.
The nerves, with their rapid action and curious electric phenomena, have often been called the telegraph wires of the body. Let us consider them as such. We may, then, imagine that there exist scattered all over the skin, and other parts of the body, a multitude of stations where messages of sensation are received. From each of these stations there is a wire leading first to the spinal marrow, and then up through that to the brain, where is the terminal or central office, to which messages from all the stations of the body are transmitted. We may also imagine that all over the muscles of the body there are other stations, not for the purpose of receiving messages as to the state of the muscles (though such stations also exist), but where orders for the muscles to contract are received. To each of these stations also there is a wire leading from the brain. According to the position of the muscle in the body, that wire will pass for a longer or shorter distance through the spinal marrow. We may imagine such a telegraph to be worked in the following manner. When, for instance, the foot is pinched at any point, the officials at the stations in the skin there will frame a message relating what has taken place. That message will be conveyed by the nerves up to the central office, where the brain, acting upon the information forwarded, will despatch along other nerves messages to the muscular stations of the leg. The orders conveyed by these messages will be obeyed, and the leg will be moved away from the offending object. An essentially similar process will be carried on whenever the brain, that is to say the will, executes movements of the body in consequence of information received by eyes, ears, nose, mouth, or any part of the skin, or any other sensitive portion of the frame.
But what happens when the wires are cut, when telegraphic communication is broken off between the brain and the foot, as when a man's back is broken? In order to explain the facts of tickling under such circumstances we must somewhat modify our scheme of telegraphs. We must imagine that the brain is not the sole central office, that the wires conveying messages are not continuous from the foot to the head, but that, on the contrary, there are in the spinal cord several, probably very many, intermediate stations which we may call spinal stations, and which receive messages from the foot, read them off, and then send them on to the brain, or perform a similar duty towards messages passing from the brain to the muscles. Just as a message sent to Suez arrives there by being passed on from one station to another, so messages running to and fro all over the body are passed on by a greater or smaller number of the spinal stations. Hence when the central office is isolated by disease or violence from the rest of the body, or when its business hours are over, or when its officers are asleep, or otherwise engaged, the intermediate spinal offices, having read the message sent by the foot, take upon themselves in an awkward, imitative manner to send orders straight off to the muscles, without troubling the brain, and so move the leg. And we may suppose that something very similar takes place even in ordinary tickling, when we are fully conscious of what is going on, and are quite aware that we are receiving peculiar sensations and executing peculiar movements in spite of all we do to prevent it. In such cases we may imagine that there is some special connection between certain stations in the skin-namely, our ticklish places, and certain spinal stations whereby the latter are authorized on receipt of a message at once to make a demand upon the muscles, merely forwarding a copy of the message to the brain.
Certain muscles, or sets of muscles, are more particularly connected in this manner, through the spinal cord, with certain spots of skin, and thus tickling brings about, not disorderly movements, but a concerted action, having an apparently definite purpose-viz., the thrusting aside of the offending object, or removal of the part affected from its neighbourhood. Under certain circumstances, however, when the part tickled is peculiarly sensitive, or when the object tickling is unusually active, or exerts itself in some unusually powerful manner, or when the spinal marrow is in what may be called an excitable state, a simple message may produce such an effect upon the spinal stations that they transmit orders in the most urgent and tumultuous fashion to almost every part of the body, and so bring about what is generally called a convulsion. Whenever this occurs, however, there is something wrong—some disease. During health a most marked purpose is always to be seen in the movements consequent upon tickling. Thus, when the nose is tickled, a sneeze ensues, with the view to drive out the offending body; when the throat is tickled, there is a cough or a retching; when the eye is touched, the eyelids close : in all these cases there is a sensation, and a consequent movement, with a definite purpose, in which brain is not necessarily concerned, may, indeed, be totally unaware of the whole matter. There are some forms of tickling, however, in which the brain is a prime mover; namely, those in which an idea, or some mental process, is the exciting cause. Thus, a ridiculous idea starting in the mind will pass from the brain, or, rather, from some part of the brain, to some station which is not the chief office of the will, and there give rise to the involuntary movements which we call laughter. A sorrowful idea will give rise to wailing and weeping ; a painful one to a cry. All these symbols of passion are kinds of tickling, though they have no evident purpose, beyond that of expression.
There are, also, other results of tickling besides muscular movements. When there is weeping, there are also tears; and the eye may be made to pour forth its secretion, without any mental affection, through a process of pure tickling by a little grit or sand. In the same way, food in the mouth, or in the stomach, produces saliva or gastric juice, by tickling the salivary glands in one case, and the lining membrane of the stomach in
the other. There are probably for these actions little special systems of telegraphs, more or less independent of the great central nervous system represented by the brain and spinal cord.
Nor have we yet exhausted the store of instances of tickling, or, as the physiologists say, of reflex nervous action, occurring in the animal economy. The channels through which that precious fluid, the blood, rushes over the body—the beautifully constructed blood-vessels, are guarded, especially the smaller arteries, by circular bands of muscles. These muscles, stretched over the hollow tubes like a crowded row of living India-rubber rings, by contracting and relaxing, can narrow or widen the pathway of the blood. When they widen, the blood, driven by the heart, rushes on impetuously, like a crowd when gates are thrown open, When they narrow, the blood-current tarries, like a crowd passing through a narrow passage. It will, on reflection, be easily seen how much the vital processess going on in any part of the body, dependent as they are to so large an extent on the quantity of blood passing through their territory, will be affected by the behaviour of the muscles of the arteries—how they will be stirred up when these relax, how they will slacken when these are tightened. All these arterial muscles are totally independent of the will, but are in abject obedience to the laws of tickling. No man can make his face blush by any effort of the will; but an idea of shame starting in the brain will readily convey an order along the nerves, and, in an instant, the muscles of certain arteries are relaxed, and ears, and face, and neck are red all over. A feeling of fear strikes a man, forthwith all the arteries of his skin are tightened, the surface of his body feels the lack of the warm blood, he himself is a-cold, and the sensations of the skin being carried back to the spinal chord, issue again in another form of tickling, and the man is said to be shivering with fright. Or, again, perhaps some trouble, some inflammation, some disease is setting in. The hidden wrong, lurking somewhere in his frame, acts, through tickling, first on his arterial muscles, thence on his skin, and so, at last, back again on his whole muscular system, and there comes over him a chill, the precursor of illness.
Indeed this tickling, whose most open mark is laughter, works wide and deep throughout the whole of our life. It often turns up were we least expect it. Thus it explains the changes of colour in chamelions and frogs. Frogs, as is well known, change colour a good deal, from a light yellowish green to a dull dark hue, which is almost black. This is caused by little patches of pigmentlittle chambers one might almost call them, full of black dots. Sometimes the dots or granules are scattered all over their chambers, in the shape of great strag. gling stars. At other times they are heaped up in a little
round ball in the centre of each chamber. When they are spread out, so that star almost touches star, the frog looks quite black; when they shrink up as dots they are hardly visible amid the yellowish green ground colour. The curious thing is that the dots or granules have themselves the power of moving like the granules of the amoeba, which the chambers closely resemble, and still more curious, they are under the influence of the nervous system of the animal, and subject to the laws of tickling. Most susceptible are they to the influence of the creature's eyes, or rather to the influence of light working through the creature's eyes. Tickle the animal's eyes with light, put him in full sunshine, and all the granules close, the skin is yellowish green. Cease to tickle his eyes-that is, shut him up in the dark, and the granules spread out again, the skin is black. That the skin is affected thus indirectly through the eyes, and not directly by the action of the light upon itself, is shown by the fact that when the poor creature's eyes are destroyed, his skin becomes black for ever, let the sun shine as bright as it will. Strange, is it not, that skin and eyes should be thus closely bound together? Yet grooms have for a long time been able to tell blind horses by their coats. In fact, we catch here glimpses of actions and processes, hidden dealings in the work of life, of which we are as yet well-nigh wholly ignorant. When we consider that every moment of our lives a stream of sensations is continually pouring in upon our eyes, our ears, our almost every part; when we reflect that all these impressions cannot go for nothing, cannot be lost, but that, on the contra?:y, every jot and tittle that enters our frame must, at some time or other, and in some form or other, go out again; and being in, must do some work, must affect, if in ever so slight a degree, the sum total of the body; we may form some idea of the multitude of messages that are for ever flashing through us, and may learn to regard with respect, as being a type of deeper mysteries, even so absurd a thing as “ Tickling."
MR. BROWNING'S LATEST POEMS.*
It gives us hearty satisfaction to perceive that Mr. Robert Browning's latest poems have already reached a second edition.
* Dramatis Persone. By Robert Browning. Second Edition. Chapman & Hall. 1864.