As to cramp, those chiefly are liable to it who plunge into the water when they are heated, who remain in it till they are benumbed with cold, or who exhaust themselves by violent exercise. Persons subject to this affection must be careful with regard to the selection of the place where they bathe, if they are not sufficiently skilful in swimming to vary their attitudes, and dispense instantly with the use of the limb attacked by cramp. Even when this does occur, the skilful swimmer knows how to reach the shore by the aid of the limbs which are unaffected, while the uninstructed one is liable to be drowned.
If attacked in this way in the leg, the swimmer must strike out the limb with all his strength, thrusting the heel downward and drawing the toes upward, notwithstanding the momentary pain it may occasion; or he may immediately turn flat on his back, and jerk out the affected limb in the air, taking care not to elevate it so high as greatly to disturb the balance of the body. If this does not succeed, he must paddle ashore with his hands, or keep himself afloat by their aid, until assistance reach him. Should he even be unable to float on his back, he must put himself in the upright position, and keep his head above the surface by merely striking the water downward with his hands at the hips, without any assistance from the legs.
PROCEDURE WHEN IN THE WATER, AND USUAL MODE OF FRONT SWIMMING.
Entering the Water.
Instructors should never force young swimmers reluctantly to leap into the water. It would be advisable for delicate persons, especially when they intend to plunge in, to put a little cotton steeped in oil, and afterwards pressed, in their ears, before entering the water. This precaution will prevent irritation of the organ of hearing. In entering, the head should be wetted first, either by plunging in head foremost, or by pouring water on it, in order to prevent the pressure of the water driving up the blood into it too quickly, and increasing congestion. The swimmer should next advance, by a clear shelving shore or bank, where he has ascertained the depth by plumbing or otherwise, till the water reaches his breast; should turn towards the place of entrance; and, having inflated his breast, lay it upon the water, suffering that to rise to his chin, the lips being closed.
Buoyancy in the Water.
The head alone is specifically heavier than salt water. Even the legs and arms are specifically lighter; and the trunk is still more so. Thus the body cannot sink in salt water, even if the lungs were filled, except owing to the excessive specific gravity of the head.
Not only the head, but the legs and arms, are specifically heavier than fresh water; but still the hollowness of the trunk renders the body altogether too light to sink wholly under water, so that some part remains above until the lungs become filled. In general, when the human body is immersed, one-eleventh of its weight remains above the surface in fresh water, and one-tenth in salt water.
In salt water, therefore, a person throwing himself on his back, and extending his arms, may easily lie so as to keep his mouth and nostrils free for breathing; and, by a small motion of the hand, may prevent turning, if he perceive any tendency to it. In fresh water, a man cannot long continue in that situation, except by the action of his hands; and if no such action be employed, the legs and lower part of the body will gradually sink into an upright position, the hollow of the breast keeping the head uppermost. If, however, in this position, the head be kept upright above the shoulders, as in standing on the ground, the immersion, owing to the weight of the part of the head out of the water, will reach above the mouth and nostrils, perhaps a little above the eyes. On the contrary, in the same position, if the head be leaned back, so that the face is turned upwards, the back part of the head has its weight supported by the water, and the face will rise an inch higher at every inspiration, and will sink as much at every expiration, but never so low that the water can come over the mouth.