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time, in diseases of chronic debility—in chlorosis, asthma, paralysis, &c.; but its use has been long abandoned.

Protoxide of Azote.—This gas, which consists of the same constituents as atmospheric air,—oxygen and azote,—but in different proportions, is possessed of very singular properties. It is the dephlogisticated nitrous air of its discoverer Priestley, the nitrous oxide, protoxide of nitrogen, or laughing gas; the last name having been assigned to it by reason of its properties.

Sir Humphry Davy first showed, that, by breathing a few quarts of this gas from a silken bag, for two or three minutes, effects, resembling those produced by drinking intoxicating liquors, are excited; yet it does not produce the same effect on all individuals, as might, indeed, have been expected. It is strange, however, that although the evidence in Sir Humphry Davy's "Researches" was most overwhelming; and although it is annually breathed in the chymical rooms of this country and Great Britain, by hundreds of students, and even made the subject of itinerant exhibition, the French chymists assert, that, in all cases in which they have tried it, it has simply produced indisposition. In the very last edition of his Chymistry, Thenard affirms, "tous ceux a qui je l'ai vu respirer s'en sont trouvés mal," and professor Pelletan, in his " Dictionnaire de Chimie," remarks—that "In England several persons have exhibited a kind of delirious gaiety, to such an extent, that it was necessary to snatch away the bladder, that contained the gas; debility and syncope soon, however, succeeded this primary state of excitement (!!) In France, in the experiments of Vauquelin and Thenard, vertigo, head-ache and protracted lassitude were alone experienced; and in no case could it be respired more than a few minutes."

The only way of accounting for these results is by the supposition, that these distinguished chymists must have had idiosyncrasies, which caused them to be affected differently from most other individuals; or that the gas was impure; and that the promulgation of the fact of indisposition having succeeded the respiration of the gas in a few cases has deterred others from having recourse to it.

In his "Researches" on this subject, Sir Humphry Davy has given the autographies of several eminent individuals relative to the effects produced upon them. Sir Humphry himself breathed four quarts of nitrous oxide from, and into, a silk bag. His first feelings were those of giddiness; but, in less than half a minute, the respiration being continued, they diminished gradually and were succeeded by a sensation, analogous to gentle pressure on all the muscles, attended by a highly pleasurable thrilling, particularly in the chest and extremities. The objects, around him, became dazzling, and his hearing more acute. Towards the last inspiration, the thrilling increased, the sense of muscular power became greater; and, at last, an irresistible propensity to action was indulged. What followed after this he recollected but indistinctly; but his motions

were various and violent. The effects soon ceased after respiration; and, in ten minutes, he had recovered his natural state of mind. The thrilling in the extremities continued longer than the other sen


Dr. Robert Southey, the distinguished laureate of England, could not discriminate between the first effects and an apprehension of which he was unable to divest himself. His first definite sensations were, a fullness and dizziness in the head, such as to induce a fear of falling. This was succeeded by an involuntary laugh, but one of a highly pleasurable character, accompanied with a peculiar thrilling in the extremities; a sensation perfectly new and delightful. For many hours after this experiment, he imagined, that his taste and smell were more acute, and he felt unusually strong and cheerful. In a second experiment, he felt still superior pleasure; and has poetically remarked, that he supposes the atmosphere of the highest of all possible heavens to be composed of this gas.

Mr. Wedgewood breathed atmospheric air first without knowing it was so. He declared it to have no effect, which confirmed him in his disbelief of the power of the gas. After breathing the nitrous oxide, however, for some time, he threw the bag from him, kept breathing on laboriously with an open mouth, holding his nose with his left hand, without power to take it away, though aware of the ludicrousness of his situation. All his muscles seemed to be thrown into vibratory movement. He had a violent inclination to make antic gestures; seemed lighter than the atmosphere, and as if about to ascend. Before the experiment he was a good deal fatigued after a long ride; but the feeling left him during the respiration of the gas.

All these and analogous effects are daily produced by the exhibiters of this singular compound; and we have seen it annually given to a class for the last seven years without any of the indisposition resulting, which has been referred to by the French chymists. There are some, however, in whom its effects are always painful.

The gas, according to the experiments of Dr. Mitchell, is possessed of considerable penetrative power. By means of this, it can readily pass through the coats of the pulmonary vessels, get into the venous blood, and produce its effects directly upon the brain, in the same manner as other intoxicating substances.

Although capable of being respired, nitrous oxide is unfit to support life. Priestley found that this was the fact, and it has been confirmed by other chymists. Mice, introduced into a jar of it, die almost immediately, whilst in azote, hydrogen, and carbonic acid, they struggle for a short time.

Hydrogen.—This gas does not appear, from the experiments of Lavoisier, Sir H. Davy, and others, to exert any positively deleterious power, when respired; and seems to destroy by excluding oxygen; hence, its effects are of a negative character. In a pure state, if the lungs have been previously emptied, as far as possible,

of atmospheric air, it can be breathed for a very short time only; quickly occasioning giddiness and a sense of suffocation; the countenance becoming livid, and the pulse sinking rapidly, followed by a state of insensibility.

When the gases were employed medicinally, hydrogen was used to diminish muscular power and sensibility, and a reduction of the force of the circulation; in catarrh, spitting of blood, consumption, &c.

Nitrogen or azote, when respired, exerts, like hydrogen, a negative influence, and proves fatal simply by excluding oxygen; an opinion, which as Bostock properly remarks, might naturally be formed respecting a substance, that enters so largely into the constitution of the atmosphere, and which, if it were possessed of any positively hostile properties, would be unfitted for its office, seeing that it is at all times received so largely into the lungs of animals.

Carburetted hydrogen gas.—This is the most active of the gases that are conceived to operate by depressing the vital functions. Even when largely diluted with atmospheric air, it occasions vertigo, sickness, diminution in the force and velocity of the pulse, reduction of muscular vigour, and every symptom of diminished power. In an undiluted state, it can scarcely be respired. Sir Humphry Davy found, that, at the third inspiration, total insensibility was induced, and symptoms of excessive debility continued for a considerable period; effects which sufficiently exhibit its positively deleterious agency. At one time, in a properly diluted condition, it was conceived to exert a beneficial effect in diseases of increased action; but it is now entirely laid aside.

Carbonic acid.—The experiments of Pilatre de Rozier and of Sir H. Davy have shown, that this gas proves more speedily fatal than either nitrogen or hydrogen; and there is every reason for believing, that it excites spasmodic contraction of the epiglottis and suffocation. Sir H. Davy found, that air was still irrespirable when it contained three-fifths of its volume of carbonic acid, but that when the proportion was diminished to three parts in ten, it might be received into the lungs. The effect, which it occasioned, after being breathed for a minute, was slight giddiness and tendency to sleep. In pneumatic medicine, it was employed as a sedative in phthisis, being diluted with atmospheric air.

Carbonic oxide or oxide of carbon appears to act in a similar manner. Sir Humphry Davy took three inspirations of this gas, mixed with about one-fourth of common air; the effect was a temporary loss of sensation, succeeded by giddiness, nausea, acute pains in different parts of the body, and excessive debility. Some days elapsed before he entirely recovered. Mr. Witter, of Dublin, was struck with symptoms of apoplexy, by breathing it, but was speedily restored by the inhalation of oxygen. It is probable, that both this gas and carbonic acid, in their pure state, occasion the closure of the glottis, and, consequently, do not enter the lungs; but, when

breathed in a more dilute condition, that they pass through the coats of the blood-vessel, and exert their action on the brain whilst circulating through it.

Sulphuretted hydrogen.—This gas is extremely deleterious. When respired in a pure state, it kills instantly, and its deadly agency is rapidly exerted when put in contact with any of the tissues, through which it penetrates with astonishing rapidity. Even when mixed with a portion of air, it has proved immediately destructive. Dr. Paris refers to the case of a chymist of his acquaintance, who was suddenly deprived of sense, as he stood over a pneumatic trough, in which he was collecting the gas.

From the experiments of Dupuytren and Thenard, air that contains a thousandth part of sulphuretted hydrogen kills birds immediately. A dog perished in air, containing roth part; and a horse in air, containing th. It is the deleterious agent exhaled from privies, which has been so fatal, at times, to nightmen, who have been employed to remove or to cleanse them.

When this gas is breathed in a more dilute state, it produces powerful sedative effects, the pulse being rendered extremely small and weak, the contractility of the muscular organs considerably enfeebled, with stupor and more or less suspension of the cerebral functions; and if the person recovers, he regains his strength very tardily.

Arsenuretted hydrogen also instantly destroys small animals, and is extremely deleterious, having proved fatal to a German chymist, M. Gehlen.

With regard to the other gases, the ammoniacal gas, muriatic acid gas, nitrous acid gas, nitric oxide or deutoxide of azote, and chlorine, they are completely irrespirable, producing spasmodic closure of the glottis, and asphyxia or suffocation.

According to the division already established, we may consider, then, that all these gases, when breathed in an undiluted condition, admit of being classed as follows:

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In concluding the subject of respiration, we may briefly ad

vert to the different modes in which the process is effected in the classes of animals, and especially in birds, the respiratory organs of which constitute one of the most singular structures of the animal economy. The lungs themselves, as in the marginal figure of the lungs, &c. of the ostrich,—are comparatively small, and are adherent to the chest, where they seem to be placed in the intervals of the ribs. They are covered by the pleura only on their under surface, so that they are, in fact, on the outside of the cavity of the chest. A great part of the thorax, as well as of the abdomen, is occupied by membranous air-cells, into which the lungs open by considerable apertures. Besides

a. Heart, lodged in one great air-cell.-b. The sto- these cells, a considerable pormach.-c. The intestines, surrounded by large air tion of the skeleton forms recepcells.-d. The trachea dividing into bronchi.-e, e.

The lungs.-1, 2, 3. ff. Other great air-cells, communi- tacles for air, in many birds; and cating with other cells and with the lungs.-g,g. The openings by which such communication is made. if we break a long bone of a bird of flight, and blow into it, the body of the bird being immersed in water, bubbles of air will escape from the bill. The object, of course, of all this, is to render the body light, and thus to facilitate its motions. Hence the largest and most numerous bony cells are found in such birds as have the highest and most rapid flight, as the eagle. The barrels of the quills are likewise hollow, and can be filled with air, or emptied at pleasure.

In addition to the uses just mentioned, these receptacles of air diminish the necessity of breathing so frequently, in the rapid and long-continued motions of several birds, and in the great vocal exertions of singing birds.

In fishes, in the place of lungs we find branchiæ or gills, which are placed behind the head on each side, and have a movable gillcover. By means of the throat, which is connected with these organs, the water is conveyed to the gills, and distributed through them; by which means, the air, contained in the water, comes in contact with the blood circulating through the gills. The water is afterwards discharged through the branchial openings,—aperturæ branchiales, and, consequently, they do not expire along the same channel as they inspire.

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Fig. 108.


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