Popular Science Monthly/Volume 29/June 1886/Scratching in the Animal Kingdom
| SCRATCHING IN THE ANIMAL KINGDOM. |
By Professor SAMUEL LOCKWOOD.
FOR nearly two weeks, one midwinter, my studies were pleasantly interrupted by a nightly visit of that funny arachnidan, Phalangium dorsatum, Say. We often hear it called Daddy-long-legs, which name in England is given only to the long-legged dipteran, the Tipula, or crane-fly. My visitor's domicile was a nook somewhere in the library. As appearances are often deceptive, it would not be safe to predicate a literary taste of my bookish visitor, but the creature's measured gait and pedal sprawl over my written page did suggest the airs of a stilted critic. And yet, to use a trade-phrase, with all its seeming bigness, phalangium did not "size up much." Its egg-shaped body was exactly a quarter of an inch in length, and an eighth wide at its thickest part. Of its eight legs, each one in the shortest pair measured an inch and five eighths, and in the longest pair the measurement exceeded three inches, a considerable spread for so little timber. There was quite a good understanding between us. It would allow me to touch the long, thread-like legs with my pen, and even to lift one up above the others, and the queer thing would keep the limb raised for several minutes, precisely as I would leave it, as if it were hypnotized.
The phalangium is a member of a tribe of the spiders known as the Pedipalpi, because the palps or feelers end, like the feet of many insects, in a claw, sometimes a pair, thus making a forceps. After my tickling his perambulators, Daddy seemed to have got his ideas started, for, having adjusted his octapodal highness upon my manuscript in most admirable equipoise, he began the delectable exercise of scratching his legs. I am sure that the operation was enjoyable to him, while to me the sight was very interesting. If Captain Cuttle should find it necessary to try the flexibility of a whip-stock, it is supposable that he would take the handle in his left hand, and with a pressing motion pass the whip for its entire length through the iron hook which served for his right hand. The whip would thus take on a loop-like curve, and would straighten itself out with somewhat of a snap. Just in this way did my spider scratch his slender legs—for one at a time were these long elastic limbs passed through the hook of the palp, when the limb would be bent like a loop or bow in the process, and as it left the hook or claw by its elasticity would do so with an almost whip-like snap.
The higher one ascends the animal scale in such observations, the more pronounced is found this habit of scratching the skin-surface of the body. Individually, Maud S. and Coomassie may be "too high-toned" for such a practice. But these creatures are coddled out of conscience by the groom, who has the comb and the brush almost always on their pelts; hence, if these "high-bloods" come not to the scratch, it is because the scratch comes to them. Cushie and Dray, put upon their own resources, enjoy hugely a good rubbing self-administered against a tree or post.
Happening one day in my lady's boudoir, I picked from the cabinet what I took for a pretty bit of bric-à-brac. It was an ebony stem, about fourteen inches long, not thicker than one's finger, and quite daintily turned. At one end was attached a pretty little hand deftly wrought in ivory. It could not be called a fist, for I noticed that the fingers were only half closed. The nails were well developed, and their ends or edges were set in a line. This artistic trifle seemed, to me made for some special purpose. A whisper from a friend enlightened my wonderment—"A back-scratch." I caught at once. Now, I have read of a toy formerly common in England, which at fairs or upon occasions of a crowd, would be passed over the back of a rustic, when it made a noise like the tearing of cloth, and suggestive of a rent behind, to the poor man's dismay. This, too, was called a "back-scratch." But that was simply the vehicle of a bit of mischief. My lady's back-scratch was for use in that very much out-of-the-way place between the shoulder-blades. This handy implement, though an article of virtu, was in the line of luxury, although the amenities would hardly approve the indulgence before eyes polite.
The above reminds how gingerly and faulty the treatment of the word is by the lexicographers. One would think it only meant to abrade, lacerate, excoriate, whereas how common the usage by which it signifies to titillate with mild friction! The Latin expresses the action nicely, scabere cutem leviter ungue, which in good English is simply—to rub the skin lightly with one's nails. Pliny has aures pedibus, scratching the ears with the feet, which suggests the experience of that tourist in Italy who rode a mangy mare. The beast had a bad habit of stopping to scratch her ears, and, the hind-feet being used for that purpose, the thighs of the rider received all the benefit of the operation, which, like tickling with a brickbat, was too crude for real comfort. But the ungulates generally are bunglers at this trick, though not insensible to opportunity, as witness when our neighbor's cow got into the lawn, and, wild with delight, went tearing through the soft evergreens, our pretty arbor-vitæ trees, which was so much nicer than rubbing against a fence.
It behooves to confess that Nature has been a niggard in this matter unto man, having done less for him in this line than she has for the beasts that perish. "The paragon of animals" is the victim of irritation from eczema in a hundred forms and degrees. Though having already thrown a stone at the lexicographers, here goes another, for we must cite from memory that churlish dictionary-maker, Dr. Johnson, who wrote in the first edition of his dictionary, "Oat—a grain used in England to feed horses; in Scotland, men." This was very unbecoming. But the food has much to do with the condition of the cuticle. Hence we put together the Scotsman's "oaten cakes" and the legend of the benevolent nobleman who set up scratching-posts in the streets of Edinburgh, and the canny benediction of each user of them, "God bless the Duke of Argyll!"
On the physical or rather physiological side of the question, a good deal might be said for this mild friction of the skin. Near the surface—that is, just under the scarf, or epidermis—the capillaries, almost microscopic blood-veins, abound in well-nigh infinite numbers. Each of these minute carriers or distributors of the crimson life-stream has along its sides its complement of nerves nearly parallel. Between these nerve-fibers lies the undifferentiated protoplasm, or life-stuff, which is the supply of constructive matter for the use of these tiny builders, for out of this life-matter, or bioplasm, each cell is built. But even mortar may need quickening—so this life-stuff may become too passive, that is, quasi torpid. These nervous fibrillæ are the electric wires, and gentle friction is the dynamo to generate the mysterious fluid and quicken the conductivity along the lines.
Strange to say, this scratching has also its psychological side. Let a puzzle be propounded, and why on the instant does the nonplused one institute a rummaging for an idea in the hirsute thatch of his cranium? And everybody does it, even he "of the front of Jove himself" more than the beetle-headed clown. We asked an explanation of our encyclopedic friend who "knows it all," and quoted to him the well-worn distich:
"Be mindful, when invention fails,
To scratch your head and bite your nails."
Upon the word he began disheveling his carefully brushed hair, saying it was "a poser," and, by way of compliment, that it "was not slow"; to which our response, "No, it's Swift"; at which he laughed, though he had quite missed the point, for he rejoined that he always thought us "a little fast."
It is truly wonderful how lavishly and admirably Nature has gifted many animals for this very exercise of scratching lightly with the claws. At my feet lie Tom and Dick, two good friends. The former is a fine young Maltese, the latter an old black-and-tan. The cat's claws are very sharp, the dog's are less so. Both animals are clean and in good condition, yet both appear to take delight in a good scratching at the back of the head, and especially behind the ears. The hind-foot is the instrument used, and with what delicacy—yes, nicety, or precision of adjustment! So rapidly does that foot move, that it makes a fan-like shadow; and so exact the distance at which the keen, protruded claws are set, that it secures only a delicate touching of the parts, producing the pleasant titillation of the tonsorial brush. Any coarser adjustment of those needle-pointed hooks and the blood would flow from the lacerated skin.
But, even more than with the mammals, is this cuticular titillation a necessity with the ordinary fishes; and, since they have neither hands nor feet, how is this want in their case gratified? I have witnessed the operation many times, yet fear a failure to adequately describe it. The scaly coating of a fish needs an occasional cleaning, as does the copper sheathing of a ship; for, with both, a foul surface impedes progress through the water. On each side of a typical fish is a thin line, known as the lateral line. It is, in fact, a mucous canal, from which issues at the will of the animal a lubricating fluid, which, spread over its scaly sheathing, lessens friction, and so facilitates movement in the water. This mucous line is made up of rows of pores, which communicate with the slime-secreting glands. Leydig discovered that each of these oil-producers had its own nerve, thus constituting a series of sense-organs. And very delicate is their sense, as by them the fish gauges the weight of the water-mass, also the direction and resistance of currents. But associated with these nerves arranged in tufts, or buttons, are air-cells, hence it seems certain that the fish is able to appreciate vibration in water, whose wave-lengths are larger than are those of sound. The faculty of appreciating the waves of light, we call seeing, and similarly of sound, hearing, whose waves are much larger than those of light. But our scaly subject is endowed with a third wave-measuring sense, in which possession it out-paragons "the paragon" himself. It can appreciate the trills or waves of water vibration, and of this faculty our language has no word to express the name.
Now, these oil-yielding tubes above described may get clogged, or the glands become torpid. Here, then, are sense-organs to declare the state of affairs. Hence arises the necessity for the animal either to clean off its body armor, or to stimulate into activity the indolent organs. And, in fact, in other ways, fishes have their own eczema, or diseases of the skin. Sometimes there is a blistering or deterioration of the cutis, and sometimes a species of Saprolegnia, a fungous parasite, sets up a floculent growth on the cuticle. For any of these instances friction is the only remedy, and its exercise is unquestionably pleasant to the fish.
But how can a fish scratch itself? Sometimes in the way of Cushie, as when she rushed through the evergreens. So a fish will often dart through a dense clump of soft water-weeds. But this amounts to little else than a gentle titillation. The scaly sheath is not to be cleansed so easily. I have seen the performance many times, and by several species, but none have so much interested me in this respect as the sunfish. Take the one best known to the pin-hook anglers, and often called "pumpkin-seed." There is a bowlder with a smooth, clean surface. The fish is steady; its big eyes seem of a sudden to glow with a blue light. Every fin is set, even to the dorsal, which bristles with its keen spines. The fish seems aiming for that stone. The propulsion must come from the caudal and the side fins, but mostly from the former. All these give a simultaneous blow against the water; at the same time, as if it were in the way, the top-sail—that is, the dorsal—falls and is snugly reefed. All this is done in a moment, and such the force that the fish truly darts, threatening to butt its nose against the rock. The speed is high, but, just ere the rock is reached, there is a marvelously sudden bend of the body, the most convex point being the exact spot which is to be scratched. Though very rapid, so well-timed is the movement, and so nice the adjustment of the position, that the pressure or amount of rub or friction is correctly received, and the point of impact is precise, and the body glances from the rock. The collision is so accurately gauged that no harm is done. And similarly, and with a great variety of ingenious posturing, the fish subjects all parts of its body to this treatment. It even contrives to scratch the top of its head, by bringing the desired spot into the proper position at the precise moment of the glancing impact with the stone. The feat is delicate and deftly, as if an acrobat should in his somersaults comb his hair against a rock with no harm done every time.
Having enjoyed the use of a large aquarium for the study of fishes, it has been an object with me to anticipate their wants. Hence I have purposely given them scratching-stones properly adapted to their needs. I was surprised that a favorite object for this purpose was a large live river-mussel, the Anodonta excurvata. The corrugations of the shell, which mark its growth, form a series of smooth ridges, upon and against which, with their contortions of twists and bends and tilts, these fishes glance in scratching themselves. As to ichthyic emotion, one can not say much. That they enjoy these exercises, I am sure; and I almost think they know their benefactor, for they come at his call at feeding-time—though up to this present writing I have not observed anything that might be interpreted as a grateful recognition of benefits conferred; certainly nothing commensurate with the canny benediction, "God bless the Duke of Argyll!"
