Page:Popular Science Monthly Volume 22.djvu/792

772 You know that, if we should put a horse under a bell weighing sixty thousand kilogrammes, it could not make its cover move at all. That is because the animal can not insinuate itself under the edge of the bell, and is not formed to raise weights with its head. But fix a lever under the edge so that the horse can work conveniently at its longer arm, and require him to raise the weight, not to a proportionate, but to an equal height with that to which the insect raised his board in the same time, and he would not fail to achieve the task.

The interest of the problem before us does not lie singly in learning why insects are capable of efforts which appear enormous as compared with their size. The important thing is to discover whether Nature, as has been said, has regarded them more favorably than it has the vertebrates and man, and has endued them prodigally with muscular force, while it has been parsimonious to the other animals. We need not believe anything of this kind. The prodigies of force that astonish us are due to a very simple cause, and can be accounted for under the common law that, of two muscles having the same mass and the same energy, the shorter one is capable of raising the more considerable weight. We may figure muscular fiber as a spiral spring, habitually relaxed, which, under nervous action, flies back upon itself. Suppose this fiber to be a decimetre long and capable of contracting to half its length, and that it has attached to it a weight, say, of a centigramme. Under the nervous action, it will raise this weight half its length, or five centimetres. Now, if we replace this single fiber, a decimetre long, by a muscular bundle weighing just as much but composed of ten fibers a centimetre long, we can attach a centigramme weight to each of these fibers, or ten centigrammes to the whole bundle; but the weight will be raised, under the contraction of the muscle, only five millimetres instead of five centimetres. What we have gained in power we have lost in extent of motion. That is the rule. We have hence a right to conclude, that short muscles have the peculiarity, as compared with long muscles of the same volume, that they act more slowly but can move more considerable masses. Consequently, small animals perform, absolutely, slower motions, but, in compensation they can move proportionately heavier masses. We can thus comprehend how our insect can move masses a hundred times heavier than itself, without having to infer that it is a hundred times stronger than a horse. Introducing its head and corselet under the obstacle it desires to remove, it stretches its six legs, raises its body, and develops an apparently surprising force. Really, it has lifted the obstacle only in the slightest degree, but enough to allow it to escape. Its strength has been furnished by the short and thick muscles of its six legs and its neck. These considerations furnish the key to all the Herculean labors performed by small animals. The smaller the animal, the more capable it is of great efforts; only it loses in speed what it develops in force. Hence the strongest insects are generally the slowest.