RESPIRATION. 



fpecting the nature of thefe fleams he forms no conjecture. 

 He obferved alio, that the air in which an animal had re- 

 fpired for fome time, was confidcrably 'diminifhed in volume, 

 an effect which he attributed to the lofs of part of its elalli- 

 city or fpring. The contemporaries of Boyle, for the 

 mo'il part, coincided with him in his ideas refpedting refpi- 

 ration ; there were, however, fome philofophcrs who fup- 

 pofed, that befides the addition of thefe vapours, the air, 

 during its continuance in the lungs, imparted fomcthing to 

 the blood. Among thefe, the firft in point of genius and 

 originality was Mayow of Oxford. He inveftigated the 

 properties of the air, and the effects produced upon it by 

 refpi ration, with great acutenefs, and concluded, that a 

 peculiar volatile fpirit, which was one of the conftituents 

 of the atmofphere, was abforbed by the blood during its 

 pafTage through the lungs. Borelli, Lower, Willis, and 

 others, adopted opinions in many refpects fimilar to that of 

 Mayow ; they imagined, that either a portion of the whole 

 mafs of air, or fome particular conftituent of it, was ab- 

 forbed by the blood, and by this means converted this fluid 

 from the venous to the arterial Hate. But fo little real 

 knowledge was at this time pofTeffed reflecting the com- 

 pofition of the atmofphere, that they entirely failed in 

 their attempts to afcertain the nature of the matter ab- 

 forbed, and their hypothefes appeared fo extravagant, and 

 fo little founded upon truth, that their doctrines fell into 

 difcredit, became negleded, and at length were totally for- 

 gotten. De Motu Anim. p. 2,7. prop. 113. De Corde, 

 p. 159—165. Willis, Pharm. Rat. p. ii. p. 34. 



Dr. Hales devoted much of his attention to this fubject, 

 and performed many experiments with a view to illuftrate 

 the manner in which the air is affected by the lungs ; he 

 concludes nearly as Boyle had done, that it acquires a noxi- 

 ous vaptjur, and that its elafticity is dimimflicd. (Statical 

 Efl'ays. ) The learned Boerhaave confefles his inability to 

 explain the changes which the air experiences by refpira- 

 tion. (Prselea. t. 5. p. 169, et feq.) The opinion of 

 Haller was not materially different from that of Boyle and 

 Hales ; he had collected all the different theories which 

 have been advanced upon this fubject, and after reviewing 

 them with his accuitomed candour and perfpicuity, he con- 

 cludes, that the air, when it is emitted from the pulmonary 

 veficles, is combined with a quantity of water, and a pecu- 

 liar noxious vapour, and has its elafticity diminifhed. 1 Notse 

 ad Boerhaav. Preled. t. 5. p. 170. Element. Phyfiol.) 

 Such was the imperfect ftate of our knowledge, when 

 Haller wrote his Elements of Phyfiology ! This noble 

 monument of induitry and genius was fcarcely publifhcd, 

 when Dr. Black commenced his experiments upon fixed 

 air, and among other interefling difcoveries, fatisfactorily 

 proved, that this peculiar gafeous fubflance is generated in 

 the lungs during refpiration. 



" So early as the year 1757," fays this diftingutfted 

 philofopher, " I convinced myielf, that the change pro- 

 duced in wholefome air by breathing it, confifts chiefly, if 

 not folely, in the converfion of part of it into fixed air; 

 for I found, that by blowing through a pipe into lime- 

 water, or a folution of cauftic alkali, the lime was pre- 

 cipitated, and the alkali rendered mild." (Black's Lec- 

 tures, by Robifon, v. 2. p. 87.) At iod, Mr. 



Bewley detected the formation of carl," in refpira- 



tion by a method fomewhat fimilar: he found, that 

 breathing through an int'ufion of litmus, the fame , 1 

 to a red colour was produced in it, as when it was expi 1 I 

 to the action of fixed air ; and wh n, by adding a I w 

 drops of the water of potaffa, the blue col hit was refl 11 I 

 to the infufion, it could again be made to difappear by fuper- 



faturating it with the acid expired from the lungs. Prieftley 

 on Air, v. 5. p. 383. 



The particular fubflance which conflituted the wholefome 

 part of atmofphcric air, was not, however, known to Dr. 

 Black a' the time his experiments were made : and long 

 before the compound nature of the atmofphere was afcer- 

 1 lined, it had been fuppofed by many philofophers, that, 

 to ufe the language of bifhop Berkeley, " there was no 

 fuch thing as a pure iimple element of air. There is," he 

 adds, " fome one quality or ingredient in the air on which 

 life more immediately and principally depends. What that 

 is, though men are not agreed, yet it is agreed it muff be 

 the fame thing that fnpports the vital and the common 

 flame ; it being found that when air, by often breathing in 

 it, is become unfit for the one, it will no longer ferve for 

 the other. This quality of the air is neceflary both to 

 vegetables and animals, whether terreftrial or aquatic ; 

 neither beafts, infects, birds, nor fifhes, being able to fubfilt 

 without air : and when air is deprived of this ingredient, it 

 becometh unfit to maintain either life or flame, even though 

 it Ihould retain its elafticity." ( Sins, § 143, et feq. 2d 

 edition.) Dr. Hooke afferted, that this ingredient or fub- 

 flance, inherent in, and mixed with the air, is like, if not 

 the very fame, with that which is fixed in faltpetre, by 

 which, during combullion, inflammable bodies are diflolved. 

 (Microfiraphia, p. 103.) The fame opinion was afterwards 

 held by Willis, Lower, and Mayow, all of whom likewife 

 conlidered the nitrous quality of the air to act an important 

 part in lefpiration. The latt author, in particular, made 

 experiments precifely fimilar to thofe which have lately been 

 brought forward to prove, that both by the burning of a 

 candle, and other combuftible bodies, and by the refpiration 

 of animals, the nitro-aerial particles of the air were ex- 

 haufted, whereby the volume of air was diminifhed, and 

 the refidual air was unable afterwards to fupport either 

 life or flame. (Tractat. Quinque, p. 98, et feq.) The 

 exhibition, however, of this peculiar, or nitro-aerial, part 

 of the air in a diftinct and feparate form, we owe to the 

 genius of Schecle and Dr. Priellley, who dilcovered, inde- 

 pendently of each other, in the year 1774, pure or dephlo- 

 giiticated air or oxygen gas. The atmofphere, which, until 

 this period, had been regarded as a homogeneous elementary 

 body, was difcovered by thefe celebrated experimenters, to 

 be compounded of two aeriform fluids, pollefling diftinct 

 properties, and having totally different purpofes in the 

 economy of nature. Thefe fubftances, which have fince 

 obtained the names of oxygenous and azotic gafes, were 

 found to exift in the atmofphere, in the conftant proportion 

 of about 22 to 78. This great difcovery, and the ufe which 

 he made of it, enabled Dr. Prieftley to propofe the firft con- 

 fident explanation of the phenomena of refpiration that had 

 ever been offered to the public ; and, although the theo- 

 retical opinions on which that explanation was partly 

 founded, no longer exill, yet it (hould never be forgotten 

 that his experiments and diieoveries firft pointed out the 



true path of inveftigation ; and have contributed, in a pre- 

 eminent degree - , to advance our knowledge of this mod 

 important function. The caufe of the unfituefs of air, beyond 

 a cerl mi extent, to fupport life and Same, lie proved to 

 arife from the deftruction of its pure part, or what has fince 

 called its ox] ■ ga : ana lie concluded, that, in re- 

 fpiration, combullion, and calcination, which, in confequi nee 

 hie peculiar theory, lie ftiles phlogiftic proceffes, itunder- 

 sifely the fame changes. Philof. Tranf. 1776. 

 Obf. on Air, v. 3. p. 9. 



About a year after the publication of Dr. PrielUcy's 



experiments, the celebrated and unfortunate Lavoilier pre- 



4 fented 



