The specific gravity of the human body is very little greater than that of water; for though the muscles and the bones are heavier (the one being 1.085, the other 2.01), the fat (0.92) is specifically lighter, and the air within the thorax tends to establish an equilibrium. Owing to this, a very slight exertion enables one to keep himself at the surface of the water; but any part of the person, as an arm, raised out of the fluid, acts like a weight imposed upon the rest of the body, and thus inexperienced persons are often drowned by their own struggles. Death takes place from asphyxia; the blood in the lungs being unchanged by the action of air, the circulation through these organs is obstructed, and the blood becomes charged with carbonic acid; insensibility is rapidly induced, and death takes place, frequently preceded by convulsive movements. The period during which the submersion may continue without death varies in different persons. (See Diving.) In some instances bodies submerged but a minute, in despite of all attempts at restoration, have been found completely lifeless, while many cases are on record in which recovery has taken place after a submersion of five minutes.

In the " London Medical Gazette," vol. xxxi., a case is given of recovery after 14 minutes' submersion; the time here was calculated, but the circumstances render the calculation exceedingly probable. The explanation of recovery after prolonged submersion has been sought in the occurrence of fainting at the moment of the fall, and it is certain that during syncope the demand for air is very much diminished. - When the body is recovered a few hours after drowning, the skin is cold and pale, presenting sometimes patches of livid discoloration; the expression is placid, the eyes half open, the pupils dilated, the tongue swollen and pressed forward, and the lips and nostrils covered by a mucous froth; the fingers are sometimes found torn and abraded, and the hand grasping gravel or other substances which have been seized in a convulsive struggle at the bottom. Internally the body presents few appearances which are characteristic of the mode of death; of these the presence of a mucous froth, sometimes stained with blood, and perhaps of a little water in the trachea, and of water in the stomach, are most noteworthy.

The water contained in the stomach appears to be swallowed previous to death; after death the apposition of the sides of the oesophagus prevents the entrance of water into the stomach. When the body is recovered after a short immersion in the water, efforts for resuscitation should be made immediately, and perseveringly continued until recovery takes place or the case is evidently hopeless. In a case related by Mr. Bloomfield 1 1/2 hour elapsed before there was any appearance of returning animation; and in one by Dr. Douglas ("Medical Gazette," vol. xxxi., p. 449), success was met with only after 8 1/2 hours. The plan proposed by Dr. Marshall Hall in 1855 is based on physiological principles, and has been found eminently successful in practice. His rules are as follows:

1. Treat the patient instantly, on the spot, in the open air, freely exposing the face, neck, and chest to the breeze, except in very severe weather. 2. Send with all speed for medical aid and for articles of clothing, blankets, etc. I. To clear the throat. 3. Place the patient gently on the face, with one wrist under the forehead. All fluids, and the tongue itself, then fall forward, and leave the entrance into the windpipe free. II. To excite respiration.' 4. Turn the patient slightly on his side; apply snuff or other irritant to the nostrils; and dash cold water on the face, previously rubbed briskly until it is warm. If there be no success, lose no time, but apply the third rule. III. To imitate respiration. 5. Replace the patient on his face. 6. Turn the body gently but completely on the side, and a little beyond, and then on the face, alternately, repeating these measures deliberately, efficiently, and perseveringly, 15 times in the minute only. (This number of thoracic movements per minute agrees with the natural order of respiratory thoracic dilatations and contractions, corresponding with a slow movement of the heart, averaging something less than 60 pulsations per minute, and therefore merits due attention.) The rationale of the operation is this: When the patient reposes on the thorax, this cavity is compressed by the weight of the body, and expiration is promoted; when he is turned on the side, this pressure is removed, and inspiration is facilitated. 7. When the prone position is resumed, make equable but efficient pressure along the spine, removing it immediately before rotation on the side. (The first measure augments expiration, the second commences inspiration.) IV. To induce circulation and warmth. 8. Continuing these measures, rub the limbs upward, with a firm pressure and with energy, using handkerchiefs, etc. 9. Replace the patient's wet clothing by such other covering as can be instantly procured, each bystander supplying a coat or waistcoat.

Meanwhile, and from time to time, proceed to the fifth rule. V. To excite inspiration. 10. Let the surface of the body be slapped briskly with the hand? or, 11. Let cold water be dashed briskly on the surface, previously rubbed dry and warm.