RESPIRATION. 



with the blood. It is conveyed to the lungs, and lofes part of 

 its carbon, or is partially animalized. It is then distributed 

 through the fyftem, and, in the extreme veffels, along with 

 carbon, parts with fo much hydrogen, oxygen, nitrogen, 

 and other elements, as to leave carbon predominant. 



It might be fuppofed, that in any view, fuch as that which 

 has been now given, there muil be fome difficulty in conceiv- 

 ing that oxygen gas mould combine with carbon with fo 

 much facility, at a temperature much lower than that which 

 is in general necelfary for their union, and this, too, with 

 the intervention of the coats of the velfels through which 

 the blood circulates. On attending, however, to the objec- 

 tion, it will be found to have no real force. Although 

 carbon, in its folid and infulated form, requires to be raifed to 

 a high temperature to caufe it to combine with oxygen, yet 

 when it makes part of a ternary or quaternary combination, 

 in which ftate its cohefion no longer oppofes the combination, 

 it is abltracted, and combined with oxygen at any natural 

 temperature. It is thus that many vegetable and animal 

 fubilanccs, when humid, are altered byexpofure to the air, 

 and carbonic acid formed. Blood itfelf is acted upon in this 

 manner. It fuffers a change precifely fimilar to that which 

 it undergoes in the lungs, and this more or lefs rapidly, and 

 to a greater or lefs extent, according to the quantity of 

 oxygen prefent, and the degree of agitation ufed. Arte- 

 rial blood was expofed by Fontana to atmofpheric air for 

 three minutes, when no perceptible alteration was occalioned 

 in the purity of the air : they were then agitated together 

 for three minutes : the volume of air was diminimed and its 

 purity impaired. When oxygen gas was fubllituted for at- 

 mofpheric air, the alteration was (till more confiderable, its 

 purity being diminifhed when agitation was avoided ; and 

 when it was agitated, the diminution in purity and volume 

 was Hill greater. In all thefe experiments, carbonic acid was 

 alfo produced. (Opufcules Phyliques, pp. 334, 335.) They 

 therefore prove, that oxygen can attract carbon from arterial 

 blood. With venous blood, the formation of carbonic acid 

 is, according to Luznriaga, Hill greater. (Differtatio Inau- 

 guralis, p. 53, 54.) If, therefore, oxygen can abitract carbon 

 from the principles of the blood, under fuch circumftances, 

 it is evident it muft do fo ltill more rapidly during refpira- 

 tion, where the circumllances are fo much more favourable, 

 where there is comparatively a high and uniform tempera- 

 ture kept up, where the blood is expofed on an extenfive 

 furface, and in a ftate of extreme divifion, and where that 

 furface, as well as the air itfelf, are rapidly renewed. 



Nor can it be fuppofed, that the thin membrane which 

 forms the coats of the veffels through which the blood circu- 

 lates can oppofe an obllacle to this reciprocal action. 

 Every humid fabftance is permeable through its whole fub- 

 Itance to elaftic fluids, and is penetrated by them. Animal 

 brane, in a much denfer ftate than that which forms the 

 .-outs of the extreme blood-veffels, is, when humid, pervious 

 to gafeous fluids ; and what is in point in the prefent cafe, 

 through fuch membranes, when humid, oxygen can act on 

 id, and communicate to it the florid colour, the lame 

 as when blood is freely expofed to it. Thus, Priellley found 

 by experiment, that if a quantity of black blood were in- 

 clofed in a moiltened bladder, which was tied very clofe, on 

 hanging it in a free expofure to the air, it 'acquired " a 

 coating of a florid colour, as thick as it would have acquired 

 if it had been expofed to the open air ; fo that this mem- 

 brane had been no impediment to the action of the air on 

 the blood." Mr. Hunter mentions a fimilar experiment : 

 •» I covered," fays he, " the mouths of veflels filled with 

 venous blood with gold-beaters' fkin, touching the furface of 



the blood, and the blood conilantly became of a flor ; d red on 

 the furface, and even for fome depth." (Treat aeon the Blood, 

 p. 62.) Nor is there any reafon to believe, as has been con- 

 tended, that in the living folids this property is fufpended, 

 for it is one connected merely with mechanical Structure, and 

 the influence of humidity. The blood, therefore, may be 

 conlidered, when circulating in veffels fo fine, as expofed to 

 the adtion of oxygen nearly as if no membrane were inter- 

 pofed : a part of that oxygen approximated to it will com- 

 bine with a portion of its carbon, and the carbonic acid, when 

 formed, will, from its elafticity, recede and be difcharged. 

 The whole action is purely chemical, and precifely the fame 

 as that wliich is exerted between air and blood out of the 

 body, favoured only by the circumflances of expofure, tem- 

 perature, and agitation, under which it takes place." P. 502. 



After adverting to the arguments, by which it is fhewn 

 that no gas can pafs through the membranes of the bronchial 

 cells and pulmonary veflels from without, nor any fubftance 

 pafs from within through thefe parts, to unite in the lungs by 

 ordinary chemical affinity, confequently that the carbonic 

 acid is not formed by the union of carbon and oxygen in the 

 blood ; and to the facts, in which carbonic acid is formed in 

 the lower animals and even in man, by the fkin, where we 

 have no proof of any abforption of oxygen, or paffage of it 

 through the animal textures, Mr. Ellis declares his opinion, 

 in which we entirely coincide, that the carbon lupplied in hu- 

 man refpiration is truly an animal excretion, performed by the 

 exhalent veffels, which exill in fuch wonderful numbers in 

 the lungs ; confequently, that it depends primarily, like 

 other excretions, on the due circulation and diltribution of 

 the blood, and is more or lefs affected by all its variations- 

 The changes in its quantity have been found very confider- 

 able, according as the individual was at reft or in motion, 

 faffing or with a full Itomach, &c. in the experiments al- 

 ready noticed of Lavoifier and Seguin. We conceive, then, 

 that the carbon, thus exhaled or excreted in the lungs, com- 

 bines in the air-cells with the oxygen of the atmofphere to 

 form the carbonic acid expired. 



As theemillion of carbonic acid in refpiration is carried 

 on through the whole period of living action, and is eflential 

 to the continuance of it, fome ulterior fource mult be pro- 

 vided, from whence its fupply maybe duly maintained. 



" To the organs of digeltion, affimilation, and Secretion 

 alone, we are enabled to trace it ; but the mode in which it 

 is reduced to that ftate in wliich it is afterwards expelled by 

 thefurfaces of the lungs and (kin, involves a knowledge of 

 the nature and qualities of our food, of the various and fuc- 

 ceffive changes which it is made to undergo in the fyltem, 

 and of its diltribution by the blood to the different organs 

 of fecretion, according to the fcveral ulcs which it is after- 

 wards deftined to anfwer : concerning all of which (objects, 

 we have of late fucceeded in getting rid of much error and 

 abfurdity, but have not in any lndancc attained to complete 

 knowledge." Ellis's Inquiry, ch. 5. 



V. On the Refpiration of the different G.iju.—Ho aeriform 

 fluid, fays Dr. Bollock, except" the compound ot oxygen 

 and azote which exifts in the atmofphere, is adapted to the 

 permanent fupport of life. Of the other gales, there are loan 

 whkh, on account of their irritating nature, it is ablolutely 

 impofliblc to receive into the trachea ; thefe properly con- 

 ithute the nonrefpirable gafes. There are, however, others 

 whkh it is poflible to infpire, though their employment is 

 followed looner or later by the extinction of life. We 

 (hall detail fome of the principal experiments that have been 

 performed on this fubject, as the nature oi the change pro. 



