In Death from Suffocation the heart continues to pulsate for several minutes after the breathing has entirely ceased, in consequence of which the blood which passes through the pulmonary vessels no longer receives the influence of oxygen, and therefore _black_ blood circulates; the brain, it would appear, soon feels the want of the florid arterial stream, by which alone its energies can be maintained. _Bichat_ has shewn that when dark coloured blood is injected into the vessels of the brain, by means of a syringe connected with the carotid artery, the functions of the brain become immediately disturbed, and, in a short time, entirely cease; the effect is precisely similar, whether the dark coloured blood be transmitted to the brain by the syringe of the experimentalist, or by the heart itself. It is not until after the full effects of the suspended respiration are thus produced on the brain, that the motions of the heart become enfeebled, and that the ventricles contract less powerfully, and at longer intervals; at length, the action of the heart is altogether arrested, and if the thorax be examined at the instant that the circulation has ceased, nothing is observed, except a slight tremulous motion of the auricles; the cavities of the left side are much contracted, and contain only a small quantity of blood, while the right auricle and ventricle, and the large vessels communicating with them, are distended to an unusual size. This state of the heart, it will be observed, is very different from that which we have described as constantly occurring after _Syncope_. In the contemplation of these phœnomena, a question very naturally suggests itself in regard to the probable interval which elapses between the cessation of respiration, and the consequent failure of the heart’s action; in other words, it may be asked, how long can the heart support its contractions without the aid of respiration? It would appear that this interval not only varies in duration in different animals, but even in the same animal under different circumstances, such as that of age,[25] capacity of the thorax, quantity of air in the lungs, state of the stomach, and general vigour of the animal; but in man, under the most favourable circumstances, it is extremely doubtful whether the heart ever continues to pulsate for so long a period as five minutes[26] after the lungs have ceased to perform their office; and it is very questionable whether, in most instances, the interval is not considerably shorter than this. BY DROWNING.