they quickly lose all appearance of life, and remain motionless and insensible under mechanical lesion; but upon withdrawing them from the water as soon as they have fallen into this state, they revive and move spontaneously. The exciting or invigorating influence of the atmosphere in this case may serve to illustrate the action of arterial blood upon the organs of warm-blooded animals. 1. When from hemorrhage, or from feebleness of the heart's action, arterial blood is thrown with less force and in less volume than usual upon the brain, fainting is ushered in by sensations of languor and feebleness, the ears ring, giddiness ensues, consciousness is lost. If in such a case the nervous system be excited by ammonia held to the nostrils, the heart beats more vigorously; and if the patient be laid in a horizontal posture, the flow of arterial blood to the brain is facilitated: by these means the conditions which produce syncope are removed, and the fainting person revives. It deserves to be remarked, that continued faintness after hemorrhage is to be encouraged as a salutary provision in cases where we cannot directly command the flow of blood; while faintness lasts, the tendency of the blood to coagulate is considerably increased, upon the effects of which the prevention of a return of hemorrhage mainly depends. By repeated or profuse hemorrhage, an exsanguinated condition of the body is produced with alarming debility, which perhaps authorize and recommend, as Dr. Blundell has recently pointed out, the transfusion of blood in such cases, from the veins of a * De l'Influence, &c. p. 7. 100 Of the Transfusion of Blood. healthy person. The original experiment of Lower, performed about the year 1660, consisted in connecting by means of a tube an artery of one animal with the vein of another: in one instance a healthy man thus received into his system about nine ounces of the blood of a young sheep without suffering from it: but subsequently the operation being employed medicinally met with some notable failures and fell into disrepute. Dr. Blundell has made it appear that the transfusion of blood in animals of different species may be fatal; but has shown that in animals of the same species, if the operation be performed with sufficient adroitness and celerity, the blood may be successfully transferred by means of a syringe. 2. When any cause prevents the introduction of atmospheric air or of air containing oxygen into the lungs, the blood is returned unchanged to the left side of the heart, venous instead of arterial blood is thrown into the brain, and consciousness is suspended. This state is termed asphyxia; the feelings with which it commences were ascertained by Pilatre de Rosier, who placed himself in irrespirable air by entering into a brewer's tub while full of carbonic acid evolved by fermentation. A gentle heat manifested itself in all parts of his body, and occasioned a sensible perspiration. A slight itching sensation constrained him frequently to shut his eyes. When he attempted to breathe, a violent feeling of suffocation prevented him. He sought for the steps to get out, but not finding them readily, the necessity of breathing increased, he became giddy, and felt a tingling sensation in his ears. As soon as his mouth Medico-Chirurgical Trans. vol. ix. p. 50; and vol. x. p. 269. reached the air, he breathed freely, but for some time he could not distinguish objects; his face was purple, his limbs were weak, and he understood with difficulty what was said to him. But these symptoms soon left him. He repeated the experiment often, and always found that as long as he continued without breathing, he could speak and move about without inconvenience; but whenever he attempted to breathe, the sensation of suffocation came on c. Symptoms very similar appear to have been produced in one experiment of Messrs. Allen and Pepys, when the same three hundred cubic inches of atmospheric air were passed and repassed from eight to ten times through the lungs the operator became insensible. It deserves remark, that the air which had been employed was found to have gained only ten per cent of carbonic acid; so that life, it appears, would probably be lost before the entire consumption of the oxygen in the air of a confined space. Lavoisier found, however, that by repeatedly withdrawing an animal and reviving it, it might be made to consume nearly all the oxygen of a given quantity of atmospheric air before death. Otherwise birds die before two-thirds, and mice and Guinea pigs before threefourths of the oxygen of the air is destroyed. When the influence of causes which produce asphyxia is prolonged, the face becomes bloated and livid, the efforts at respiration cease, and the heart's action gradually fails. The first attempt to be instantaneously made in such a case is to inflate the lungs either with 102 Effects of breathing Nitrous Oxide. fresh atmospheric air blown with bellows into the nostril, or with air thrown from the lungs of an assistant into those of the asphyxiated person. The body as a general rule should be kept warm; but in cases from the burning of charcoal, the application of cold is said to be useful. The period is not determined at which the power of resuscitation is lost after breathing has been wholly prevented; it probably does not much exceed four or five minutes: about this time life may be considered irrecoverably gone, not merely in consequence of the continued suspension of the energy of the brain, but because the heart appears to lose its irritability when florid blood is not circulating in its vessels. The experiments of Mr. Brodie and of Dr. Wilson Philip, which have been already mentioned, show that after the removal of the brain and spinal chord the heart will continue to act for a length of time, if by means of an artificial respiration it continues to receive florid blood; but if this excitement be withheld, the tendency of the heart to alternate action and relaxation quickly ceases. 3. When nitrous oxide is breathed, although it is uncertajn in what degree and by what means the nature of the blood is modified, yet its effects upon the brain are remarkable, and illustrate in a different manner the stimulating effect of the blood. In this instance its power of excitation is increased; and phenomena frequently occur resembling those of intoxication; a degree of vertigo is experienced; the spirits are exhilarated; the muscular force appears increased, and a tendency to violent exertion ensues. When a mixture of oxygen with hydrogen is breathed, a sedative effect appears to be pro Effects of Water, Air, &c. injected into the Veins. 103 duced. On breathing oxygen nearly pure, a general glow over the body, with gentle perspiration and quickened pulse, has been observed to take place. 4. When warm water is injected into the veins of an animal after an equal quantity of blood has been drawn from its body, the animal appears enfeebled; its nervous energy appears diminished. There appear to be grounds in the temporary advantage obtained in hydrophobia by this means, according to the experiments of Majendie, for repeating the trial upon animals if not upon human beings attacked with this desperate malady. 5. If air be thrown into the jugular vein of an animal suddenly and in large quantity, a peculiar sound is heard in the chest; the animal utters cries expressive of suffering and quickly perishes. If air be introduced gradually into the veins, frequently no symptom follows. It appears that death may take place from this cause, when in surgical operations at the root of the neck the external jugular vein is accidentally opened. It has happened in such a case that air has been drawn during inspiration into the right cavity of the heart: faintness, cold perspiration, with a peculiar noise in the chest, ensued, and the patient expired in a quarter of an hourd. Medicinal substances introduced into the blood in small quantities act promptly and violently; and are thus administered in the veterinary college at Copenhagen. Oily and viscid substances introduced into the blood produce death rapidly, by obstructing the pulmonary capillaries. An American physician, it appears, tried in his own person the injection of a small quantity d |