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pute to the partial views of these very men, the greater proportion of the error with which it abounds.

If any thing, however, can contribute to render an imperfect science speedily perfect, it is the publication of inquiries conducted on the plan of those which form the subject of the present article. We scarcely know any work in physiology, where an author has displayed a more extensive knowledge of every fact contributing, in the most remote manner, to elucidate the object of his investigation; in which, he has sought the opinions of others with more diligence, or stated them with more uniform candour; or where he has himself interrogated Nature, by experiments more judicious or more successful.

It is a fact, which has been long sufficiently known, that every thing which lives, whether animal or vegetable, requires, for the continuance of its life, a constant supply of fresh air. The great purpose of Mr Ellis's Inquiry, is to discover why it is that air is necessary to the vital existence of organized bodies. In the present volumes, he has particularly in view, to show the precise nature of the changes which the air suffers, from the action of animals and vegetables upon it; and in what manner. those changes are effected. The original Inquiry' was published in 1807; but the author has, since that time, not only been led, in obviating the very few objections which have been urged to his doctrines, to the discovery of some new and interesting facts, but has corrected his original views by various additional experiments. The result of the whole we shall endeavour to lay before our readers in as few and as plain words as possible.

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In the human body, from the first to the last moments of its existence, we remark, that a certain quantity of air is alternately rushing into and out of the mouth and nostrils. The chest, or thorax, is so constructed, that, merely from the elasticity of its sides, and the pressure of the surrounding parts upon them, it has a tendency to assume a certain permanent capacity or dilatation. Accordingly, after death, when there no longer exists any counteracting cause, this is the capacity which it assumes and retains. We may call it the natural state of the thorax. In the living body, however, it is found that, by the action of the surrounding muscles, a further enlargement of the chest, beyond its natural state, may be produced. As soon as this dilatation commences, it is obvious that a sort of vacuum must be formed between the sides of the thorax and the lungs. A current of air, therefore, immediately flows through the windpipe into the air-cells of the lungs, and gradually distends these or ans, in proportion as the eavity containing them is increased.

9.117 cubic inches of oxygen; while they acquired 7.647 cubic inches of carbonic acid, by a single respiration. This conclu sion was deduced chiefly from experiments performed by Mr Davy; in which he found, that when he applied his mouth to a tube connected with a mercurial air-holder containing atmospheric air, and made a single inspiration and expiration from and into this vessel, as much in the manner of ordinary breathing as possible, the contents of the airholder were diminished in bulk, and contained less nitrogen and oxygen, and more carbonic acid, nearly in the proportions just stated. To the deductions which had been made from, such experiments, in as far as they related to the disappearance of nitrogen, Mr Ellis had objected, that they were such as the results obtained did not warrant; since there was no proof, that the chest was reduced exactly to the same capacity after as before the experiments; and we could not therefore infer, that the nitrogen gas which had disappeared from the airholder was not to be found in the lungs. We wish he had extended this obvious and substantial objection, to the inferences which had been drawn from the same experiments regarding the proportions of oxygen and carbonic acid; for it appears in all respects equally applicable to them. If a small quantity of the nitrogen of the inspired air remained in the lungs, merely because the thorax was of larger dimensions after than before the experiment, for the same reason a portion of oxygen, or carbonic acid, which otherwise would have been found in the airholder, might have been retained in these organs.

Two memoirs on this subject, the joint production of Seguin and Lavoisier, were read to the Academy of Sciences of Paris, in 1789 and 1790; and Laplace has preserved the results of those experiments, in prosecution of the same inquiry, with which the philosopher last named was engaged when he was dragged to the guillotine-experiments which he himself would have communicated to the world in detail, had not the short respite of a few days, which he requested for that purpose alone, been with such unprecedented barbarity denied. It would have been agreeable to us, if we could have attached any value to these investigations of two chemists so celebrated. But that caution which ought to be inseparable from every philosophical pursuit, precludes our placing the least reliance on results of experiments, when they are not detailed with the most circumstantial minuteness. We honour the memory of Lavoisier, and respect the talents of his surviving coadjutor. But their memoirs to which we have alluded, will hereafter be read, chiefly because they are among the last labours of one of the greatest philosophers

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philosophers of the eighteenth century. And, indeed, it is impossible to observe the tone of enthusiasm which these essays have in some parts received, from the prevailing spirit of the times in which they were written, without melancholy reflections→→ without feeling again awakened in us those emotions of deep regret with which the recollection of that period of disappointment must ever be contemplated.

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As we never can be assured that the capacity of the lungs is the same after as before the experiment, we cannot decide, with certainty, how far the relative proportions of the gases in the air expired, may not have been influenced by this cause. it is obvious, that if the diminution which may have been ob served in the bulk of air by one inspiration, depended on any natural and constant process in the animal economy, by which air is continually abstracted from the cells of the lungs, the re-, duction in volume which would take place, in breathing a large quantity of air, would be directly proportional to the number of respirations necessary to transinit the whole of this air through the lungs. Whereas, were it dependent on any such accidental circumstances as we have now alluded to, no such increase ought to be observed: the diminution might even be least, when the quantity of air inspired was largest; and, at all events, we should not expect to find it, in any instance, exceeding 20 cu bic inches, or half the bulk of an ordinary inspiration. This point has been determined, in the most satisfactory manner, by the experiments of Messrs Allen and Pepys. About three years ago, they constructed an apparatus, by which from 3000 to nearly 10,000 cubic inches of atmospheric air could be transmitted once through the lungs, by easy respirations, beginning and ending with a forced or extreme expiration: And, of thirteen experiments of this kind which they performed, the greatest de ficiency in the expired air appeared in one where 3860 cubic inches had been inspired, in which it amounted to 62 cubic inches; in another, where 3620 cubic inches had been breathed, the diminution was only 4 cubic inches; and, in a third, 9890 cubic inches lost only 18. But, although it is thus established, that there is one cause to which the diminution is not owing, we do not feel ourselves entitled to assert, positively, that, in all these instances, it ought to be ascribed solely to the difference between the extent of the expiration immediately preceding, and of that closing the experiments. It may, hereafter, be shown to be dependent on circumstances entirely different. In the mean time, it may be remarked, that even the greatest deficiency in these experiments was not equal to half the differonce between an ordinary and an extreme expiration.

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this gas out of the cells of the lungs, it combined only with a small portion of it, the remainder passing back into the cells again; while others thought it more probable, that no more was absorbed by the blood from the cells, than this fluid perma nently retained.

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This rapid and easy transmission of gases through the sides of the cells and vessels of the lungs, which is the common foundation of all these theories, Mr Ellis maintains, is not only totally devoid of proof, but, if sound philosophy only allows us to conjecture, respecting phenomena unseen, from what we have experienced of similar events actually perceived, that it is not legitimate to entertain it, even as an hypothesis. Dr Lower had indeed observed, that when dark-coloured blood was brought into contact with atmospheric air, it assumed a florid colour; and various other physiologists after Priestley, had proved that this, or any other air containing oxygen, so exposed, lost part of its oxygen, and gained carbonic acid. Lower had also demonstrated, by experiments on quadrupeds, that the change of colour from modena to a scarlet red which the blood underwent in the lungs, depended entirely on the presence of fresh air in their cells: And Priestley found, that when a quantity of dark-coloured blood was tied up closely in a moistened bladder, and hung in the air, the whole lower surface of the blood acquired a coating of a florid red colour, as thick as if no bladder had intervened. From all this, it had been inferred, that, dur ing respiration, either some part of the air passed through the sides of the cells and vessels of the lungs into the blood, or that something was given out by the same course, from the blood to the air, so as to alter the colour of the one, and the composition of the other. But, without denying that, in these instances, the change of colour in the blood depended on the presence of atmospheric air, or of air containing oxygen, Mr Ellis has shown, by the most satisfactory experiments, that, in the case where the bladder intervened, neither did the air afford any portion of its gases to the blood, nor did the blood communicate any matter to the air. Thus, when he put a quantity of black blood into a small bladder, and suspended it in a glass jar containing 13.1 cabic inches of atmospheric air inverted over mercury, he found that the blood soon reddened; that, at the end of two days, the whole of the oxygen of the included air had disappeared-but that an equal quantity of carbonic acid had been formed. Hence it is obvious, that as all the oxygen which had disappeared was converted into carbonic acid, none could have penetrated the bladder, or combined with the blood. On

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the other hand, when Mr Ellis suspended, in the same manner, bladders filled with water, or bladders empty, but moistened, in jars of atmospheric air, the oxygen was equally found to be converted into carbonic acid. Since, therefore, it thus appears that a moistened bladder is of itself capable of affording carbon to form carbonic acid with the oxygen of the air, there is no reason for supposing, that the carbon is derived from any other source, where the bladder is filled with blood; and the conclusion seems irresistible, that when dark-coloured blood is reddened by the air, through the sides of a moistened bladder, the air yields no oxygen to the blood, nor acquires from it any carbon; but the carbon of the bladder, by its combination with the oxygen of the air, passes into the state of carbonic acid gas. The doctrine, then, of the entrance of gases into the blood from the air cells of the lungs, can no longer be regarded as receiving the best support from Priestley's experiment. But although the result had been otherwise, and the direct passage of something through the bladder had been unequivocally proved, we should still have been disposed to maintain with our author, that it would not necessarily follow, that any similar transmission of air took place through the sides of the cells and vessels of the lungs. On the contrary, we regard it to be a fact, as well established as any in Physiology, that no part of the body, provided with vessels, however delicate it may be, has ever been observed to permit the smallest quantity of kind of fluid to permeate through it, as long as the circulation continues in that part; though, as soon as death has taken place, transudation goes on in all textures with the utmost facility. We should not, therefore, be entitled to infer, merely because a dead bladder may seem to allow of the transmission of air, that the cells and vessels of the living lungs are equally permeable to that fluid.

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Mr Davy had concluded from experiment, that 71 or 93 cubic inches of nitrous oxide might, in the short period of half a minute, be absorbed by the venous blood, through the moist of the pulmonary veins. Our author's observations, alone, would have left very little doubt in our minds, that, in these experiments, though a portion of gas had disappeared from the airholder, none had passed into the vessels of the lungs. But we have, ourselves, found, by repeated trials with nitrous oxide and atmospheric air, that, when a given quantity of either of these is frequently breathed, the desire, or sympathetic stimulus to inspire, becomes gradually so strong, and the expirations proportionally so short and restrained, that, at last, when the ex

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