which the function of respiration is performed. The influence which the air exerts, is always upon the circulating fluid or blood. It produces some change in it, or imparts some principle to it, which renders it fit to be distributed to the body for its nourishment. In all the animals, which have red blood, viz. the Mammalia, Birds, Reptiles, and Fishes, this change consists, so far as can be observed, in imparting to the dark red or venous blood, which is sent to the lungs by the heart, a bright red or vermilion color. In this state, it is returned to the heart, and thence distributed throughout the body by the arteries.

'In the Mammalia, the air is alternately drawn into the lungs and expelled from them, by the action of the diaphragm and muscles of the ribs. This is called the inspiration and expiration of the air, and is constantly going on in order to produce the requisite change upon the blood, which is continually passing through the lungs. In the greater part of the animals of this class, if this process be stopped but for a few moments, death is the inevitable consequence; but in some species it may be suspended for a longer period. This is the case with the seal and the whale. Even men may acquire by habit the power of existing a considerable time without breathing, as is the case with the fishermen who dive for pearls ;* but many of the stories which have been related with regard to this subject, are probably destitute of foundation.

'There are many other kinds of air or gas, which may be taken into the lungs, beside the atmospheric; but no other, which will support life. Even pure oxygen itself, and another gas which contains oxygen, although they will support life longer than any other kinds of air, will yet finally prove fatal. It is only when oxygen is combined with azote in the proportion above mentioned, that it is adequate to the continual support of life. The quantity of air ordinarily contained in

The pearl-fishers have been said to remain half an hour or more under water. The accounts, however, which state so extraordinary a fact as this, must be looked upon with great doubt. It seems impossible, from what we know on the subject, that any human being could exist and remain capable of action under water, more than a few minutes.'

'Water destroys the life of animals merely by preventing the admission of air; it does not itself enter the lungs, or at most only in a very small quantity. There are some gases which operate in the same way. The windpipe is spasmodically closed against them, and they do not enter the lungs; such are carbonic acid gas, ammoniacal gas, chlorine or oxymuriatic gas, &c., when unmixed. Other gases are inspired with sufficient ease, but produce death, either merely for the want of oxygen, as hydrogen and pure azote; or, in a certain sense, by poisoning the blood or destroying its vital properties, as carburetted and sulphuretted hydrogen, and carbonic oxide. Oxygen alone, as has been remarked above, and nitrous oxide, which

the lungs of a common-sized man, immediately after an inspiration, has been calculated to be about two hundred and eighty cubic inches, and about forty inches are drawn in and thrown out at each inspiration and expiration; so that the whole mass of air is not changed at every breath, but a large proportion remains constantly present, and distends the lungs.

"If the air which has been respired be examined, a change will be found to have taken place in its composition. A part of its oxygen has disappeared, and in its place is found about the same bulk of carbonic acid or fixed air. There is also a considerable quantity of watery vapor. This change is undoubtedly connected with the effect produced upon the color of the blood in respiration; and many have endeavored to give some account of the mode in which it takes place. But it is a process which we shall probably never be able fully to understand. A similar change is produced upon the air respired by all animals of whatever class.

'Respiration has been supposed to be the cause of animal heat. Various opinions have been advanced to account for the manner in which it maintains the temperature of our bodies. None of them, however, seem perfectly satisfactory. It appears undoubtedly to have some very close connexion with respiration, and dependence upon it; for the degree of heat in animals is generally proportioned to the vigor and quantity of respiration. The temperature of birds is higher than that of man, and they consume a greater quantity of air. Reptiles and fishes have cold blood, and the amount of respiration in them is comparatively small. The same remark is true of all cold-blooded animals. But we are not yet acquainted with the exact nature of the connexion between respiration and animal heat.*

Respiration commences immediately after birth, and at the same time a change is produced in the course of the cir

contains a greater proportion of it than atmospheric air, are capable of supporting life for a considerable period, but finally prove fatal. The latter is celebrated for its intoxicating and exhilarating effects, when respired.'

*Animal heat has been supposed to arise from a chemical action taking place in the lungs at the time of the change of venous blood into arterial, in the same way that heat is produced by many other chemical operations; but if this were true, the lungs ought to be hotter than any other part of the body, which is not the case. It has been also supposed to arise from a greater capacity for caloric in the arterial, than in the venous blood, in consequence of which, heat would be developed when the change from the former to the latter takes place in the capillary vessels of the body. This is more probable, but still hardly satisfactory. Neither of these hypotheses accounts for the independent temperature of eggs, which resist cold so long as they retain their life; nor for the power in men of resisting very high degrees of heat, with hardly any increase of the temperature of their bodies.'

culation. Before birth, only a very small proportion of the blood is carried through the lungs; but after birth, and through life, the whole of it. The connexion between the action of the lungs and that of the heart, is very close and important. The functions they perform are mutually dependent, and neither can go on alone. If the circulation cease by the cessation of the action of the heart, respiration is immediately interrupted. If, on the other hand, respiration be impeded, the heart does not stop at once; but as the dark, venous blood is no longer changed in its properties, as usual, in the lungs, it is returned to the heart in the same state, and is then sent throughout the body; and being totally unfit for the purposes of life, destroys it, by cutting short the action of all the organs. The effect of its contact upon the brain, is an immediate suspension of life; and if the cause be long continued, it is never restored. But in many cases of this kind, as in persons apparently drowned, circulation and respiration may be renewed, if they have not been too long interrupted, by blowing air into the lungs, and by the application of warmth and stimulating substances to the body.

'Beside these uses of the function of respiration, it is made subservient to a number of other important purposes. All animals furnished with lungs, express their wants, their affections and aversions, their pleasures and pains, either by words, or by sounds peculiar to each species. These are produced by different changes in the windpipe or canal through which the air is drawn into the lungs. The inferior animals are by this means enabled to maintain some sort of communication with others of the same species, and can, to a certain extent, convey information and express their affections and wants. But how far they are intelligible one to another, it is impossible to ascertain.' On man alone, nature has bestowed the faculty of speaking, or of expressing his various feelings and ideas, by a regular, extensive, and established combination of articulate sounds. To have extended this faculty to the brute creation, would not, it is probable, have been of any use to them; for, though some animals can be taught to articulate, yet none of them seem to have any idea of the proper meaning of the words they utter. Speech is perform= ed by a very various and complicated machinery. In speak ing, the tongue, the lips, the jaws, the whole palate, the nose, the throat, together with the muscles, bones, &c. of which these organs are composed, are all employed. This combination of organs we are taught to use when so young, that

we are hardly conscious of the laborious task, and far less of the manner by which we pronounce different letters and words. The mode of pronouncing letters and words, however, may be learned by attentively observing the different organs employed by the speaker. By this means we are enabled to correct the various defects of speech, and even to teach the dumb to speak; for dumbness is seldom the effect of imperfection in the organs of speech, but generally arises from a want of hearing; and it is impossible for deaf men to imitate sounds which they never heard, except they be taught to use their organs by vision and by touching.

When about to laugh, we make a very full inspiration, which is succeeded by frequent, interrupted, and sonorous expirations. When the titillation is great, whether it arises from the mind or body, these convulsive expirations sometimes interrupt the breathing to such a degree as to endanger suffocation. Moderate laughing, on the contrary, produces health; by agitating the whole body, it quickens the circulation of the blood, gives an inexpressible cheerfulness to the countenance, and banishes every kind of anxiety from the

mind.

In weeping, we employ nearly the same organs as in laughing. It commences with a deep inspiration, which is succeeded by short, broken, sonorous, and disagreeable expirations. The countenance has a dismal aspect, and tears are poured out. Weeping originates from grief, or other painful sensations either of body or mind. When full vent is given to tears, grief is greatly alleviated. Both laughing and weeping have been reckoned peculiar to man. But this notion seems not to be well founded. Though the other animals express not their pleasures or pains in the same manner as we do, yet all of them exhibit their pleasant or painful feelings by symptoms or cries, which are perfectly understood by the individuals of each species, and, in many instances, by man. A dog, when hurt, complains in the bitterest terms; and, when he is afraid or perhaps melancholy, he expresses the situation of his mind by the most deplorable howlings. A bird, when sick, ceases to sing, droops the wing, abstains from food, assumes a lurid aspect, utters melancholy, weak cries, and exhibits every mark of depressed spirits. By this means, animals intimate the assistance they require, or soften those who maltreat them. Their plaintive cries are sometimes so affecting as to disarm their enemies, or to procure the aid of their equals. On the other hand, when animals.

are pleased or carressed, they discover, by their countenance, by their voice, by their movements, unequivocal symytoms of cheerfulness and alacrity of mind. Thus the expression of pleasure and pain by brute animals, though not uttered in the precise manner with those of the human species, are perfectly analogous, and answer the same intentions of nature.

By respiration and the instruments employed in the performance of it, the young of animals are enabled to extract milk from the breasts of the mother. By respiration, odors are conveyed to the nose; and coughing, sneezing, yawning, sighing, singing, and many other functions of the animal economy, are at least partly accomplished.

The Respiration of Birds is carried on by an arrangement of the lungs, very different from that of the Mammalia. They are enabled to transmit air to almost every part of their bodies, by means of membranous sacks or bags, which receive it from the lungs through certain orifices or passages on the surface of these organs. The lungs themselves are firmly attached to the ribs, and are almost incapable of dilatation or contraction, but the air passes through them into the sacks by the action of the abdominal muscles. In this way it is diffused not only throughout the thorax and abdomen, but extends even to the cavities of many of the bones, which are distinguished from the others by their lightness, their white color, and the absence of any bloody matter or marrow in their cavities.

This provision answers probably several important purposes. It renders birds lighter in proportion to their bulk, than animals whose bones are filled with marrow or other solid substances, and thus gives them some advantage in flight; and generally in birds of the longest and highest flight, as eagles, this extension or diffusion of air is carried farther than in others. But a more important object of it probably is, to contribute to the muscular strength of these animals, by producing a very extensive operation upon the blood. The motions of birds in flight, require a much greater expenditure of power, than those of walking or running in other animals. This power depends upon the circulation of the red, arterial blood in the muscles which exert it, and in order to increase the proportion of this in the system, the influence of the air is carried over the whole system, instead of being confined to the lungs alone. It has been found that birds consume, in proportion to their size, more air than quadrupeds; and this arises from its extensive influence upon