RESPIRATION. 



fented a memoir on refpiration to the French Academy of 

 Sciences. (Mem. de l'Acad. des Sciences, 1777.) After 

 paying a tribute of refpeft to the genius of Dr. Prieftley, 

 he proceeds to an accurate examination of his experiments, 

 and the conclufions which were deduced from them. He 

 agrees with the doftor in fuppofing, that the proportion of 

 oxygen is diminifhed in air which has been refpired, but 

 upon a careful analyfis of the refidue, he finds it to differ 

 from the air left after the calcination of metals, which is 

 merely azotic gas, in containing a quantity of carbonic acid. 

 He alfo obferved, that the bulk of the air was fomewhat 

 diminifhed, and we learn in general from thefe experiments, 

 that the changes produced in air by refpiration, confift in 

 the removal of part of the oxygen, in the addition of a 

 quantity of carbonic acid gas, and in the diminution of its 

 volume. He fuppofes that the azote is not affefted by the 

 procefs, and that it ferves merely to dilute the oxygenous 

 part of. the atmcfphere. 



In this paper, M. Lavoifier does not mention the aqueous 

 vapour which is fo evidently difchargcd from the lungs by 

 refpiration; it is impoflible that it could have been over- 

 looked by fo accurate an obferver ; we may therefore con- 

 jecture, that he omitted to mention k, became at this period 

 he confidered it as only diffufed through the air expired 

 from the lungs, by the procefs of evaporation, and not 

 formed in confequence of the operation of any chemical 

 affinities. 



The conclufions of this philofopher refpefting the changes 

 produced by refpiration upon the air taken into the 

 lungs, are for the moll part acquiefced in by modern phy- 

 fiologiits, and the refearches which have been fince made 

 upon this fubjeft are principally directed, either to aicer- 

 tain with more precifion the proportion of the refpeftive 

 ingredients in the air of expiration, or to frame hypothefes 

 to account for the operation of the lungs in effecting thefe 

 changes. 



Among the inveftigations, however, of a date fubfequent 

 to this memoir of Lavoifier, thofe of Meffrs. Allen and 

 Pepys, publifhed in the Philofophical Tranfaftions, 1808 

 and 1809, deferve peculiar mention, on account of their 

 great accuracy, and the fatisfaftory manner in which they 

 have confequently enabled us to determine fome doubtful 

 points. 



Quantity of Oxygen con/timed. — " A difficult and interefting 

 queftion," fays Dr. Boilock, " refpefting the confumption 

 of oxygen, is the abfolute quantity of this gas confumed 

 by refpiration in a given time. The firft calculations which 

 were made upon this fubjeft, in confequence of the imper- 

 feft nature of the apparatus employed, and of the want of a 

 fufficient dexterity in the management of pneumatic expe- 

 riments, were unavoidably vague and inaccurate. The dif- 

 ficulty was much increafed by a circumftance firft noticed 

 by Dr. Crawford, and afterwards more fully inveftigated 

 by M. Jurine of Geneva, and M. Lavoifier, that the refpir- 

 ation of the fame animal in different ftates of the lyltem, 

 and under the operation of different external circumftances, 

 affefts the air in very different degrees. This curious faft, 

 which affords an infight into fome of the mod important 

 operations of the animal economy, muft unavoidably produce 

 great differences in the refults of the bell conduced expe- 

 riments, and will render it impoffible for us to arrive at 

 more than an approximation to the truth. The circum- 

 ftances which have been dif'covered to influence the che- 

 mical effefts of the refpiration are, the temperature of the 

 air refpired, the degree of mufcular exertion, the itate of 

 the digeftive organs, and the condition of the fyftem as 

 affefted by fever ; it is highly probable that other circum- 



ftances will be difcovered, by multiplying and varying our 

 experiments upon the living body." 



An experiment performed by Lavoifier, upon a guinea 

 pig, feems to have been the firft in which a perfeft appa- 

 ratus, and the neceffary degree of accuracy, were employed. 

 (Mem. de l'Acad. des Sciences, 1780, p. 401 — 8.) The 

 animal was confined over mercury, in a jar containing 24* 

 cubic inches of gas, confiding principally of oxygen, in 

 an hour and a quarter, the animal breathed with much dif- 

 ficulty, and being removed from the apparatus, the ftate of 

 the air was examined. Its bulk was found to be diminifhed 

 by eight cubic inches, and of the remaining 240 inches, 40 

 were abforbed by cauflic potafh, and confequently confifled 

 of carbonic acid gas. Taking 100 parts of this air, thefe 

 numbers will be as follows ; the air was diminifhed to 96.5, 

 or by 3.5 cubic inches, and of the remainder, 16.5 were 

 coi verted into carbonic acid gas, and abforbed by potalh, 

 h reduces the quantity of air to 80 cubic inches. 

 Towards the conclufion of the experiment, the air would 

 be neceffarily much lefs fit for performing the funftions of 

 the lungs than the air of the atmofpherc, in conlequence of 

 the carbonic acid gas which it contained ; but as the air 

 employed was originally much purer than the atmofphere, 

 the author fuppofes, that the quantity of oxygen deltroyed, 

 was probably about the fame which would have been con- 

 fumed under the ordinary circumftances of refpiration. 



The fame philofopher performed a fecond experiment 

 upon the fame fpecies of animal, with ft ill more accuracy, 

 in which pure oxygen was employed. (Ann. de Chimie, 

 t. 5. p. 261, et feq. ) This experiment continued during 

 an hour and a half, and the animal being then removed 

 from the jar, the air was analyfed as in the former cafe : 

 1728 cubic inches of air were found to be reduced to 

 1673, '• '• ' la d fuffered a diminution of 55 inches, cauflic 

 potafh abforbed about 229.5 inches, leaving a refidue of 

 pure oxygen. Thefe numbers, eftimated as in the former 

 cafe, will be nearly as follows; 100 inches were reduced 

 to 96.82, or by 3.18 inches, the potafh abforbed about 

 19 inches, reducing the whole quantity of air to 77.82 

 parts. The quantity of carbonic acid was here fomewhat 

 greater than in the former experiment, which may be attri- 

 buted to the air employed being pure oxygen, and to the 

 procefs having been continued for a fomewhat longer fpace 

 of time than in the former inflance. Upon the whole, the 

 refults correfpond as nearly as can be expefted, from the 

 very delicate nature of the experiments. 



Dr. Menzies firft attempted to afcertain the quantity of 

 oxygen confumed by a man, in the courfe of a day. He 

 lound by experiment, that one-twentieth part of air, which 

 had been once refpired, is converted into carbonic acid gas : 

 this he concludes muft have been oxygen, as that part of the 

 air alone is affefted by refpiration. He conceives that 720 

 cubic inches of air are refpired in a minute, of which con- 

 fequently 36 will be confumed. From thefe data he efli- 

 mates, that in the fpace of 24 hours, 51,840 cubic inches, 

 or 17625.6 grains of oxygen, are confumed and converted 

 into carbonic acid gas. In this calculation feveral important 

 particulars appear to have been overlooked, and accordingly 

 it ..ill be found to differ from the refults of the more accu- 

 rate experiments, which have been fince performed by M. 

 Lavoifier, and Mr. Davy. 



The experiments which were made by M. Lavoifier, in 

 conjunction with his friend M. Seguin, were condufted 

 with every pofhble attention to accuracy, and with an ap- 

 paratus more complete than any which has ever been em- 

 ployed in phyfiological refearches. An account of them is 

 detailed in two papers in the memoirs of the Academy of 



Sciences 



