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periment is terminated from fatigue, the lungs may contain, in some instances, even twice as much air as at the commence.
It is obviously from inattention to this circumstance, that Messrs Allen and Pepys, in their late investigations, have been deceived into the conclusion, that, when atmospheric air is breathed in this laborious way, a portion of oxygen is absorbě ed ;-a conclusion which, had not Mr Ellis shown it to be matter of hypothesis and not of fact, we do not hesitate to say, would have led us to doubt the accuracy, even of two of the most eminent chemists in the island.
At the present day, we believe, there are not many who suppose, that any part of the air is conveyed into the blood by the channel of the absorbent vessels: Yet Mr Ellis has thought it necessary to point out how little grounds there are for such an opinion. We are aware that experiments upon dogs have been referred to in support of it ;-in which, air, introduced into the cavities of the pleura or peritonæum, has disappeared in a few days. But we should almost have thought a reference of this nature quite unnecessary, when it is so generally known, that, sometimes, in the human body, in consequence of a very trifling laceration of the lungs from a broken rib, such a quantity of air escapes from the chest into the cellular membrane under the skin, as to blow it up over the whole surface, to the depth of nearly a foot; and yet all this air is gradually removed; so that the body, from having the appearance of a huge bladder fully inflated, in a few days recovers its natural form. Still these phenomena are far from demonstrating, that air, in an elastic state, is taken up by the absorbents of the lungs during respiration.
Having thus shown, that the fundamental principle of all the prevalent hypotheses, respecting the manner in which the air is altered by natural breathing, is inaccurate, Mr Ellis's simple and most satisfactory deduction on this point may be stated in a few words. Air, examined after respiration, is found to differ from the same air before it is breathed, in having lost a portion of oxygen,-gained an equal volume of carbonic acid, -and in being loaded with watery vapour. This additional carbonic acid, then, is either given out directly by the exhalent vessels of the lungs, or it is actually formed within the air cells. Now, it is not directly emitted from the vessels ; for in that case it ought to be discovered in the air expired, whatever the composition of the air inspired may have been: But this is not so; for no carbonic acid is exhaled when hydrogen is breathed. It must, therefore, be formed within the cells. If so, the oxygen entering into its
composition must be derived from the air inhaled; for it is not generated, unless that air contains oxygen ; and the quanțity of oxygen which is lost by the inspired air, is exactly equal to that of the carbonic acid emitted. On the other hand, the carbon with which the oxygen combines, must be supplied by the lungs ; and Physiology does not permit us to suppose, that this supply is accomplished in any other way, than by an exhalent secretion from the branches of the pulmonary artery, opening on the surface of the air cells. In what state the carbonaceous matter is secreted, whether purely as carbon, or in combination with other substances, is yet uncertain. Here, however, it may be proper to remark, that since we have estimated, that about 92160 cubic inches of carbonic acid are formed, by the direct combination of its constituent principles, within the air cells of the human lungs, in the course of 24 hours, it follows, that as much latent heat is daily set free, within these organs, as would melt 201.03 lib. troy of ice. Lastly, with respect to the water which is found dissolved in the expired air, we may observe, that we cannot regard it as formed by the union of the oxygen inhaled, with hydrogen present in the air cells; for all the oxygen which disappears is employed in forming the carbonie acid. In consistency with physiological principles, therefore, we must suppose, that it is poured out on the surface of the cells, either in the state of pure water, or holding other substances in solution, by an exhalent secretion from the vessels of the lungs.
We cannot leave the consideration of the changes produced on the air by animals proyided with lungs, without adverting to another very singular alteration, which Mr Ellis has, with great ingenuity, suggested that it may undergo, from its introduction into these organs. Messrs Allen and Pepys had found, that when they respired pure oxygen, a quantity of nitrogen considerably greater than what could reasonably have been supposed to have existed in the lungs before the experiment, was mingled with the expired air, and that an equal bulk of oxygen gas had disappeared. In like manner, when a guinea-pig was made to breathe pure oxygen, or a mixture of this gas and hydrogen, the expired air contained a volume of nitrogen much more than equal to the cubic contents of the animal's body, and had lost a proportional bulk of oxygen or hydrogen. It was observed, too, that the emission of nitrogen was always greatest in the first expiration ; and that its quantity progressively diminished, until, towards the close of the experiment, it was reduced almost to nothing. Far from regarding these plieñónienil, with
Messrs Alan and Pepys, as proving an evolution of nitrogen from the blood, and a corresponding absorption of oxygen or hydrogen, Mr Ellis infers, with more accuracy, that the nitrogen must have been derived from the residual air in the lungs, and that it has been displaced from the cells by the mere mecha nical substitution of the other gases. But if this inference be just, since a much greater volume of nitrogen was emitted, than the lungs could have contained of that gas in an elastic state, we cannot but suppose, as has been argued by our author at great length, that these organs exert, upon inspired air, a property similar to that which chemists have proved pieces of por; ous charcoal to possess, namely, a power of attracting and condensing several times their volume of atmospheric air, oxygen, hydrogen, nitrogen, and various other gases. Hence, though the lungs do not contain a greater bulk of air than has commonly been supposed, yet they may, in fact, contain a greater weight of that elastic fluid. Mr Ellis will not be displeased to learn, that this analogy had occurred, many years ago, to one of the most judicious of the French physiologists, M. Hallé. Among a list of questions connected with respiration, which he proposes for resolution, we find the following:
Dans les altérations qu'éprouve l'air dans la respiration, en est-il qu'on doive attribuer plutôt au poumon qu'au sang? • et indépendamment de l'humidité pulmonaire, la propriété
singulière qu'ont la plupart des corps spongieux d'absorber
les gaz et de leur faire perdre l'état élastique, ne peut-elle pas • entrer pour quelque chose, dans les fonctions que le poumon
remplit dans la respiration?' Encyclop. Meth. Medecine, I. 506,
Land animals of the classes of Insects, Mollusca and Vermes, and Terrestrial Oya, Larvæ and Chrysalids of Insects, operate upon the surrounding air, either by receiving it into cavities, which they can enlarge or diminish at will like lungs; or into tubes, called tracheæ, opening externally by orifices or stigmata; or the power of acting upon it seems possessed by the whole surface of the body. * There can be little doubt, from the numerous experiments which our author has detailed on bees, flies, grasshoppers, slugs, snails, earth-worms, and various larvæ and chrysalids, that all these, like man, remove, by their respiration, a certain quantity of the oxygen of the air, and substitute
* We have adopted the classification of animals, which will be Cound proposed under that article in Dr Rees's Cyclopædias
a corresponding bulk of carbonic acid, leaving the nitrogen ånaltered. But it is certain that they produce no carbonic acid, imless when in contact with air containing oxygen. It is most consistent with analogy, therefore, and it is in no respect incompatible with the anatomy or physiology of these animals, to suppose, that, in changing the surrounding air, they merely afford to it, by a process like secretion, a certain quantity of carbonaceous matter, which, uniting with its oxygen, constitutes an equal volume of carbonic acid.
The water of springs, rivers, and of the sea, always contains from 1'to ty part of its bulk of an air, composed of from 4 to 15 of oxygen, from 16 to of nitrogen, and from 105 to of carbonic acid. Now, all aquatic animals, such, for example, as the whole class of fishes, many insects, mollusca, vermes, and zoophytes, and several aquatic ova of land animals, are constantly producing changes on this air contained in their natural element. Fish act upon it through the medium of organs familiar to every one, called gills; and the animals of the other classes, either by means of organs like the gills of fish, or of tubes like the tracheae of many - terrestrial insects; or by a structure, too minute to be seen, existing on all parts of their surface. With respect to the alteration which i hey effect, Mr Ellis has quoted a variety of experiments on different kinds of fish, muscles, marine testacea, snails, leeches, zoophytes and tadpoles, in which it was found, that the water in which these animals were placed, lost a part of its oxygen, and received an addition of carbonic acid, while its nitrogen remained unaffected. It was not actually demonstrated, in these instances, that the quantity of carbonic acid produced, exactly equalled the oxygen which had disappeared; but we confidently infer, with our author, that this was the extent of the change. Nor have we Jess hesitation in concluding, that the carbonic acid was formed, by the combination of carbon separated froin the animal by the vital process of exhalation, with the
oxygen of the air contained in the water. And here we cannot refrain from quoting the beautiful provision of nature, which "Mr Ellis has developed. The experiments of Scheele and others had shown, that water possesses a superior attractive power for
oxygen ; composed, we presume, by Mr Macartney. It seems to us superior to any that has yet been offered to the public. In applying the terms Land or Terrestrial to animals, we wish them to be understood as designating those which are killed by immersion
in water, in opposition to the Aquatic class, or such as die merely from being removed out of that Huid,
oxygen ; and that, as it attracts this gas, it parts with its carbonic acid ; so that the latter never exceeds a certain quantity, in the water either of springs or of rivers. And hence, says Mr Ellis, 'the noxious gases, formed in water by the exercise • of the animal functions, and by the decomposition of organic ' bodies, are regularly expelled ; and thus the air, destined to
support the living functions of aquatic animals, like that of the atmosphere which we breathe, is maintained nearly in an uniform state of composition and purity.' $ 558.
The experiments of Hooke and Spallanzani, referred to by our author, prove, that the order of zoophytes called Infusoria, such as the animalcules of vegetable infusions, of vinegar, and of stagnant waters, are killed by placing these fluids in a vacuum, or stopping them up closely in a phial. And, in the absence of any direct proof, we may presume, that, like other animals, they exhale carbon, which combines with oxygen existing in the medium in which they live, and forms carbonic acid.
Lastly, we think it extremely probable, that those detached and apparently irritable substances, called Hydatids, so frequently discovered in diseased parts of other animals, and which might with propriety be constituted into an order of zoophytes under the name of Parasitica, act in a similar manner upon oxygen contained in the fluids which surround them.
Thus Mr Ellis has conducted us, by satisfactory experiment, and the most reasonable analogies, to this great inference, that every individual in the animal kingdom is continually exhaling carbon, to form carbonic acid with the oxygen of the atmosphere, or of the air existing in the fluids in which lives.
We should now willingly have followed our author through the various stages of his interesting inquiries into the Respiration of Vegetables. But as we have already almost transgressed our limits, we shall content ourselves with a few such remarks on his researches in this department, as we hope will induce our readers to consult the work for themselves.
In the first place, then, Mr Ellis scems to have abundantly established, both by numerous experiments of his own, and an appeal to those of preceding writers, that all terrestrial plants, whether growing in absolute darkness, in the shade, or exposed to the direct rays of the sun, are constantly removing a quantity of oxygen from the atmosphere, and substituting an exactly equal volume of carbonic acid ;--that they produce this change, by cmitting from their leaves, flowers, fruits, stems and roots, by a process like animal exhalation, carbonaceous matter, which