atmospheric air: the blood, ceasing to be purified, exerts powerfully poisonous effects upon the nervous system.

From numerous experiments, it may be inferred, that the oxygen taken from the atmospheric air is generally replaced by an equal, or nearly equal, quantity of carbonic acid gas. The average quantity of air taken into the lungs at every inspiration is about forty cubic inches. The same average quantity is thrown out during an expiration, leaving about one hundred and seventy cubic inches in the lungs; so that ordinarily these organs contain upwards of two hundred cubic inches of air. It has been wisely arranged that the lungs should not be thoroughly emptied of air by each expiration; for had they thus been collapsed, a considerable impediment would have existed to the free circulation of blood through these organs and in the event of a portion of food or other foreign body accidentally passing into the windpipe, it would not readily be dislodged; for no sooner, in the present admirable arrangement, is a sense of suffocation produced by the presence of any foreign body in the air-tube, than an effort is made by repeated and forcible expirations to expel the offending body, which effort is, happily, generally efficient. Here, then, is a merciful and wise provision against injurious and fatal effects; and simply by the presence of a quantity of air in the lungs over and above that which is directly concerned in the process of respiration.

It appears that, during the process of respiration in an individual of ordinary size and health, about twenty-seven cubic inches and a half of carbonic acid gas are given off from the lungs in the course of one minute; which, at the end of twenty-four hours, would amount to 39,600 cubic inches, or, in round numbers, 40,000; and as 100 cubic inches weigh 46 grains, 40,000 would weigh 18,532 grains. Then, since a quantity of carbonic acid gas weighing 100 grains contains 28 grains of carbon, a quantity

weighing 18,532 grains would contain 5,190 grains, or nearly 11 ounces, at 480 grains to an ounce; so that a quantity of carbon equalling two-thirds of a pound in weight, is daily discharged from the blood by means of the simple process of respiration.*

The alternate motions of the chest constituting inspiration and expiration continue from the moment of birth, during sleep or awake, till death; and, as was remarked in reference to the action of the heart, it has been wisely arranged that this should be an involuntary action, and entirely independent of the control of the being. Truly, in the language of Sir Charles Bell, "for the continuance of life a thousand provisions are made. If the vital actions of a man's frame were directed by his will, they are necessarily so minute and compli cated, that they would immediately fall into confusion. He cannot draw a breath without the exercise of sensibilities as well ordered as those of the eye or ear. A tracery of

nervous cords unites many organs in sympathy; and if any one filament of these were broken, pain, and spasm, and suffocation would ensue. The action of his heart, and the circulation of his blood, and all the vital functions, are governed through means and by laws which are not dependent on his will, and to which the powers of his mind are altogether inadequate. For had they been under the influence of his will, a doubt, a moment's pause of irresolution, a forgetfulness of a single action at its appointed time, would have terminated his existence."†

The perpetual, unceasing action: of the lungs varies in quickness according to the age, condition of health, and other circumstances, of the individual. In an adult at rest, a respiration occurs about fourteen times in a minute, or once to about

Kidd's Bridgewater Treatise, on the Adaptation of external Nature to the physical Condition of Man.

+ See Bell's Bridgewater Treatise: The Hand, its Mechanism, and vital Endowments as evincing Design.

five pulsations of the heart. Then we see that the lungs serve an ad. mirable purpose of exposing an immense surface of blood to the air. A similar arrangement of blood-vessels could not have been made so near to the air on the exterior of the body without exposing the innumerable and delicate vessels to constant injury, nor could the highly vascular surface have been preserved in a moist condition, which is necessary to the permeability of those vessels. Besides which, succession of air to each point of the surface could not have been secured. The Creator has therefore wonderfully provided an immense surface within, of the very finest texture, secure from external injury, and supplied with constant moisture, and continually exposed not oly to the external air, but to successive draughts of it.

The increased temperature which all animals, particularly those known as warm-blooded, possess above the surrounding medium, and which they maintain under every variety of external circumstance, probably depends upon the function of respiration: but the precise source of this heat has not been satisfactorily ascertained; whether it results from the chemical combination in the lungs of the oxygen derived from the air, with the carbon of the renous blood; or from the greater capacity for caloric of the arterial, being exchanged for the smaller capacity of the venous blood in the minutest blood-vessels; or from the union of oxygen and carbon in the minutest vascular extremities in every part of the body. The latter, as has been previously remarked, is most probably the situation in which carbonic acid gas is formed; but, doubtless, the nervous system has considerable influence in the evolution of animal heat. It is certain that the temperature of animals is proportionate to the energy with which the respiratory function is carried on; or, in other words, the more freely the blood is sub jected to the influence of the air in a gaseous state, the more ener getic the respiratory action, and the

higher the temperature of the ani mal. It is this circumstance which accounts for the exaltation of vitality of the quadruped and the bird above that of the reptile, and constitutes the difference between mam malia and fishes. Dr. Roget very aptly illustrates the connexion be tween aerial respiration and the temperature of warm-blooded animals, when he concludes his ob servations on animal heat, in the following eloquent language:"However the warm-blooded cetacea, who spend their lives in the ocean, may be found to approximate in their outward form, and in their external instruments of motion, to the other inhabitants of the deep, they are still, from the conformation of their respiratory organs, dependent on another element. If a seal, a porpoise, or a dolphin, were confined, but for a short time, under the surface of the water, it would perish with the same certainty as any other of the mammalia, placed in the same situation. We observe them continually rising to the surface in order to breathe, under every circumstance of privation or of danger; and however eagerly they may pursue their prey, however closely they may be pressed by their enemies, a more urgent want compels them, from time to time, to respire air at the surface of the sea. Were it not for this imperious necessity, the whale, whose enormous bulk is united with corresponding strength and swiftness, would live in undisturbed possession of the widely-extended domains of the ocean, might view without dismay whole fleets sent out against him, and might defy all the efforts that man could practise for his capture or destruction. But the constitution of his blood, obliging him to breathe at the surface of the water, brings him within the reach of the fatal harpoon. In vain, on feeling himself wounded, does he plunge for refuge into the recesses of the deep; the same necessity recurs, and compelling him again to present himself to his foes, exposes him to their renewed attacks, till he falls in the unequal struggle. His colos

eal form and gigantic strength are of little avail against the power of man, feeble though that power may seem, when physically considered, but which derives resistless might from its association with an immeasurably superior intellect." *

During healthy respiration, no sound is heard unless the ear be placed directly in contact with the chest, or through the medium of a tube. By these means, in health, a respiratory murmur, and in a diseased condition of the lungs, various sounds characteristic of the different affections to which these organs are liable, may be distinctly heard. The application of the stethoscope to the detection of diseases within the chest, and to the accurate discrimination between them, was first practised by Laennec, and has, within the last few years, opened one of the most important and extended fields for observation that ever claimed the attention of the medical practitioner.

Closely connected with human respiration are the prejudicial effects of tight-lacing; and we would briefly allude to this prevalent and destructive habit. After perusing the description of the mechanism of respiration, and reflecting on its high office in the animal economy, it will be unnecessary to explain to the reader how important it is that the movements of the ribs and expansion of the lungs should be free and unrestricted. By tight-lacing, the respiratory function is particularly interfered with, and one or many of a fearful catalogue of diseases liable to be engendered. The writer would seriously invite the attention of all classes of the community to a practice which especially exerts its baneful effects upon the young and the beautiful of female society.t

See Bridgewater Treatise, vol. ii., page 340.

For farther information on this subject, the reader may be referred to Coulson's work on Deformities of the Chest, and to a work written for the young, entitled, "The House I live in." In the former will be found an ample catalogue of diseases capable of being produced by

The process of respiration in birds differs considerably from that which is observed in quadrupeds. The lungs in birds are almost incapable of motion, being firmly fixed to the back part of the chest, and are much smaller in proportion to the size of the body; but this diminished size of the thoracic lungs is more than compensated for by the numerous membranous air-cells which occupy a considerable part of the abdomen as well as of the chest, and are found also between the muscles. All these cells communicate with each other, and with the lungs, from which latter organs they are supplied with air. The bones of birds also are hollow, and, instead of containing marrow, are filled with air, supplied to them from the air-cells before referred to. These cells are largest and most numerous in those birds which take the highest and most rapid flight, as the eagle, the hawk, and the lark; in them they are found even in the integuments of the neck, and under the blade-bones. In fishes, a very beautiful apparatus (the gills) is provided for the abstraction of air from the element in which they live; which air serves the same purpose in their economy as in our

own.

In the respiration and circulation of some of the lower animals, there is a singular torpidity in a certain season of the year: these are called "hybernating "animals. "When food is in abundance, these animals are lively and on the alert; but as it becomes more scanty, their circulation growing languid causes them to fall into that state, in which they continue during the winter months without food, and almost without life, till the period of their

tight-lacing; and in both, a view of the natural form of the chest, and as altered by this habit.

For a pleasing description of the function of respiration in birds, fishes, and insects, as well as in the human being, the reader may refer to "The Arcana of Nature Revealed; or, Proofs of the Being and Attributes of God, elicited in a brief Survey of the Works of Creation. By T, Kerns, M. D.,"

• &c.

usefulness returns, and they are again required to keep under the smaller animals on which they feed. It is remarkable that many animals, which in northern countries pass the winter in a dormant state, are not distinguished by this peculiarity in more temperate climes. The fact, that these animals become quite fat before the period of hybernation commences, and that when the time of their re-appearance arrives, they have become thin and even emaciated, proves how wisely the Creator has provided a means, out of the ordinary course of nature, for preserving his creatures in those countries at a season when no food is to be obtained."* Several of the smaller animals pass the winter in this climate in a state of occasional torpidity: they retire, and are not to be seen during the continuance of very severe weather in winter. "The temperature of animals during hybernation, although it falls proportionately with the temperature of the surrounding air, still is 4° Fahrenheit higher than it. Respiration is kept up, though slowly and almost imperceptibly. The marmot, during hybernation, breathes seven or eight times in a minute, the hedgehog four or five times, the great dormouse nine or ten times in the same period. During the state of the deepest torpor, however, respiration ceases entirely; and then the animals, if Spallanzani's observation is correct, may be placed with impunity in an irrespirable gas. Saissy found that, until this last state ensues, they continue to remove the oxygen from the air, the quantity of oxygen consumed decreasing as their temperature falls; but it still continues, together with the exhalation of carbonic acid, as long as any oxygen remains in the air; whereas animals which do not hybernate, such as rabbits, rats, and sparrows, die when they have consumed a small portion only of the oxygen of the air contained in the vessels."+

• See Burnett on the Power, Wisdom, and Goodness of God, as displayed in the animal Creation, page 307.

+ See Müller's Physiology, page 78.

In the aëration of the sap as carried on by the leaves of plants, and its subserviency to the respiratory process of animals, we notice one of the most beautiful adaptations in the whole range of the creation. The carbonic acid gas which is thrown off from the lungs of animals as a noxious agent, is necessary to the growth of plants, in the leaves of which it is decomposed, the carbon being absorbed as matter of nourishment, and added to the sap, the oxygen being emitted in a pure form into the atmosphere; whence, as beautifully written by the poet, whom natural history claims as her own,

66 in bright floods the vital air expands,

And with concentric spheres involves the lands;

Pervades the swarming seas and heaving earths,

Where teeming nature broods her myriad births;

Fills the fine lungs of all that breathe or bud,

Warms the new heart, and dyes the gushing blood;

With life's first spark inspires the' arganic frame,

And as it wastes, renews the subtle flame."

In the dark, carbonic acid gas is given out by plants, and oxygen absorbed, but in much smaller proportion than in the reversed operation during the day. At the season of the year, too, when vegetation is most active, the days are much longer than the nights; so that the diurnal process of purification goes on for a greater number of hours than the nocturnal process by which the air is vitiated.

"When we consider," says one of our most elegant writers, "that vegetation carpets all the surface of our globe; and that its shrubs and forests still occupy the largest portion of its superficial extent; and when we find that it is universally, by day and by night, streaming from its verdure-from every leaf, fruit, and flower-an aërial fluid of

See Sir James Smith's Introduction to Botany.