Man can sustain himself upon the water, and traverse it for a considerable space by swimming; but this is not an instinctive method of locomotion for him—he must learn to swim, while walking and the other modes of progression are natural to him, and are not acquired by study. Man walks, runs, and jumps just as an amphibious animal swims without having learned to do so; but to swim he must study the attitudes and the movements which neutralize the effect of his specific gravity, which prevent him from sinking into the water, and permit him to gain a resting-point in order to displace it.

The quadruped swims as if walking in the water, that is, by making just the same movements as in walking on the ground. Man can, it is true, swim as animals walk, striking the water with his four members; but he is soon overcome by fatigue, and to swim for any length of time he must execute other movements considerably complicated in their combinations. It is from that modest amphibian, the frog, from which he borrows in this case the method of progression, and this loan is certainly the most inoffensive of all those which he makes from the animals. Although he seems to turn his members quite away from their normal functions, he soon attains the power of prolonging this exercise, which is eminently healthful and very precious, since he finds in it a means of saving his own life and the lives of his fellowmen.