MODE OF DEATH IN DROWNING.
Since various lesions may be found, accordingly as the death from drowning has taken place from one or more of the foregoing modes, it is necessary to have a clear notion of asphyxia and to study in detail the mechanism of arrest of the thoracic movements and of the hindrance to hæmatosis.
Broadly speaking, there will be asphyxia when any obstacle hinders air from entering the pulmonary vesicles, or when the fluid that penetrates them is of any other nature than the medium in which the animal is destined to live. Consequently the name asphyxia is applied generically to all accidental conditions in which life is threatened by any intervention whatever of the respiration. (See Mechanical Suffocation, Vol. I., p. 705 et seq., and Asphyxiating Gases, Vol. IV.)
Submersion in any liquid medium causes asphyxia. This condition may be caused on being surrounded by a medium devoid of oxygen and improper to support sufficient hæmatosis, as hydrogen, nitrogen, and the protoxide of nitrogen, gases not toxic properly speaking, but considered irrespirable. Diminished respiration from deficiency of oxygen is the true cause of asphyxia. No animal can maintain the respiratory process in an atmosphere devoid of oxygen or in one that does not contain at least ten per cent of this gas, and such quadrupeds as whales, hippopotami, and seals or the pygopodous birds would drown in the same manner as a dog if kept submerged long enough. The suppression of the gaseous exchange by submersion is also fatal to such aquatic insects as hydrophiles, dytiscidæ, and the like, which drown in the same manner as the hymenoptera, coleoptera, diptera, or other terrestrial insects. Ants drown in less than a minute when the body is wet, and the disappearance of apparent vitality is accompanied by convulsive movements indicating functional trouble of the nervous apparatus. Sir John Lubbock found that after eight hours of immersion they could be restored to life, and several ants after two days and five days were restored to momentary life with feeble motions, followed by death in two hours. Even a terrestrial plant when submerged drowns like a terrestrial animal, the mechanism of asphyxia by submersion being the same in plants and aerian animals, and due to closure of the principal way of gaseous exchange.
Notwithstanding the interruption of the gaseous exchange necessary to support life, there is long persistence of vitality after submersion of some creatures in which an intra-molecular respiration or gaseous dialysis with aerated water takes place, as in ants who have not been wetted before submersion.
The resistance of new-born animals to this mode of asphyxiation is especially noted in the greater time required to drown a pup than an adult dog. One minute and a half usually suffices to drown a dog, while a new-born pup often requires as much as fifty minutes. This great difference is owing to the less active change of tissue and the smaller consumption of oxygen in the young animal. The more active the vital combustion and the greater the demand upon the general store of oxygen in the blood, the quicker the young animal perishes when the respiration is obstructed.
It is observed in a general way that all kinds of death caused by the privation of respirable air have between themselves the greatest resemblance. Whatever be the obstacle that intercepts the connection of the lungs with the atmosphere, the apparent differences are only secondary and the essential symptoms are identical, because all act in suppressing the functions of the blood and hæmatosis. In fact, the phenomena of asphyxia are constant and related to disturbances in the respiration, innervation, and circulation, which vary according as the asphyxia is the result of submersion or of the absence of oxygen in the surrounding medium, according as asphyxia is immediate or slow. The fatal result of asphyxia is owing to the introductory arrest of the pulmonary circulation, the capillaries of the lungs being incapable of conveying venous blood. The stagnation of the blood in the lungs is followed by paresis of the respiratory centre and stoppage of the heart.