Naturalist. Comparison of Strength of Large and Small Animals.

Manawatu Standard, Volume IX, Issue 7, 6 December 1884, Page 1 (Supplement)

Naturalist. Comparison of Strength of Large and Small Animals.

W. N. Lockington. M. Delbetjf, m a paper read before the Academic Royale de Belgique, and published m the Revue Scicntique, reviews the attempts of various naturalists to make comparisons between the stfength of large animals and that of small ones, especially insects, and shows that ignorance or forgetfulness of physical laws vitiates all their conclusions. After a plea for the idea, without which tho fact ia barren, M. Delbsuf repeats certain statements with which readers of modern zoological science are tolerably familiar, such as the following :— A flea can jump two hundred times its length ; therefore, a horse, were its strength proportioned to its weight, ; could leap the Eocky Mountains, and a whale could spring two hundred leagues m height. An Amazon ant walk. 1 ? about eight feet per minute, "but if the progress of a human Amazon were proportioned to her larger size, she could stride over eight leagues an hour ; and if proportioned to her weight, she would make the circuit of the globe m about twelve minutes. Thi3 seems greatly to the advantage of the insect. What weak creatures vertebrates must be is the impression conveyed. But the work increases as tho weight. In springing; walking, swimming, or any other activity, the force employed has first to overcome the weight of the body. A man can easily bound a height of two feet, and he weighs .as much- as a hundred thousand grasshoppers, while a hundred thousand grasshoppers could leap no higher than one — say a foot. This Bhows that the vertebrate has the advantage. A man represents the volume of fifteen millions of ants, yet can easily move more than three hundred feet a minute, a comparison which gives him forty times more power, bulk for bulk, than the ant possesses. Yet were all the conditions compared, something like equality would probably be the result. Much of the force of a moving man is lost from the inequalities of the way. His body, supported on two points only when at rest, oscillates like a pendulum " from one to the other as he moves. The ant crawls close to -the ground, and has only a small part of the body unsupported at once. This economises force at each step, but on the other hand multiplies the number of steps so greatly ■ since the smallest irregularity of the surface is a hill to a crawling creature, that the total loss of forco is perhaps greater, since it has to slightly raise ifcs body a thousand times or so to clear a space spanned by a man's one's step. By what peculiarity of our minds do we seem to. expect the speed of an animal to be m proportion to its size. We do not expect a caravan to move faster than a single horseman, nor an eight hundred pound shot to move twelve thousand eight hundred times farther than an ounce ball. Devout writers speak of a wise provision of Nature. " If," say they, " the speed of a mouse were as much less than that of a horse as its body is smaller, it would take two steps per second, and be caught at once." Would not Nature have done better for the mouse had she suppressed the cat ? Is it not a fact that small animals often owe their escape to their want of swiftness, which enables them to change their direction readily ? A man can easily overtake a mouse m a straight run, but the ready change of direction baffles him. M. Plateau has experimented on the strength of insects, and the facts are unassailable. He has harnessed carabi, neci ophori, June-beetles (Melolontha), and other insects m such a way that, with a delicate balance, he can measure their powers of draught. He announces the result that the smallest insects are the strongest proportioned to their size, but that all are enormously strong when compared bulk for bulk with vertebrates. A horse can scarcely lift two-thirds of its own weight, while one small species of June- beetle can lift sixty-six times its weight ; forty thousand such June-beetles could lift as much as a draught-horse. Were our strength m proportion to this, we could play with weights equal to ten times that of a horse. This seems, again, great kindness m Nature to the smaller animal. But all these calculations leave out the elementary mechanical law : " What is gained m power is lost m time." The elevation of a ton to a given height represents an expenditure of an equal amount of force, whether the labor is performed by flea, man, or horse. Time supplies lack of strength. We can move as much as a horse by taking more time, and can choose two methods— either to divide the load or use a lever or a pulley. If a horse moves half ■■'" f s own weight three fest m a second, whil^ a June-beetle needs a hundred seconds to con/ey fifty times its weight an equal di3tame, the two animals perform equal work proportioned to their weights. True, the cockchafer can hold fourteen, times its weight m equilibrium (one small June-beetle sixty-six times), while a horse cannot balance nearly his own weight. But this does not measure the amount of oscillatory motion induced by the respective pulls. For this, both should operate against a spring. A small beetle can escape from under a piece cf cardboard a hundred times its weight. Pushing its head under the edge and using it as a lever, it straightens itself on its legs and moves the board just a little, but enough to escape. Of course, we know a horse would be powerless to escape from a load a hundred times its own weight. His head cannot be made into a lever. Give him a lever that will make the time he takes equal to that taken by the insect, and he will throw off the load at a touch. The fact is that m small creatures the lack of muscular energy is .replaced by time. Of two muscles equal m bulk and energy the shortest moves most weight. If a muscular fibre ten inches m length can move a given weight five inches, ten fibres one inch long will move ten times that weight a distance of half an inch. Thus smaller muscles have an absolutely slower motion, but move a greater proportional weight than larger. The experimenter before mentioned was surprised to find that two grasshoppers, one of which was three times the bulk of the other, leaped an equal height. This was what might be expected of two animals similarly constructed. The spring was proportioned to tho bulk. In experiments on the insects with powerful wings, such as bees, flies, dragon-flies, &c, it was found that the weight they could bear without being forced to descend was m most cases equal to their own. In some cases it was more, but the inequality of rate of flight, had it been taken into the reckoning, would have accounted for this. Take two creatures of different bulk, but built upon exactly the same plan and proportions, say a Brobdignagian and a Lilliputian, and let both show their powers m the arena. Suppose the first to weigh a million times more than the second. If the giant could raiee to his shoulder, some thirty-five feet from the ground, a weight twenty thousand pounds, the dwarf can raise to his shoulder, not; as might be thought, a fiftieth of a pound, but two full pounds. The distance raised would be a hundred times less. In a race the Lilliputian, with a hundred skips a second, will travel an equal distance with the giant, who would take but a skip m a second. The log of the latter weighs a million limes the most, but has only ten thousand times as

many muscle fibres, each a hundred times longer than those of the dwarf, who thus takes one hundred skips while the giant takes ono. The same physical laws apply to all muscles, so that, when all tho factors are considered, mn?eles of tho quality havo pcmp.l power. — Am. Field.