Page:Popular Science Monthly Volume 29.djvu/260

248 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