RESPIRATION. 



with the atmofphere. The tube, were large, and valves, air and apparatus employed, or the refiftance which this 

 with tne atraoipi e a m create tQ thg ordl proce f s , W ill greatly vary 



upthtlube "JK5 JSS to fe°M4 fo that the refu^ and confiderable errors -ft likewife have arifen 

 upright tuoe, ffow f _ efcapc from the vanaUon ln bulk> occafioned by the change of 



into the atmofphere, 



having once entered it, 



covering the mouth and noilrils, to prevent any air 



•, when expelled from the lungs, mould not efcapc 



nor return from the allantoid, atter 



Precautions were taken alfo, by 



from 

 3ut of the lungs, except by the tubes above 

 mentioned. Things being thus prepared, he began to re- 

 fpire, and did not remove his mouth from the tube till he 

 had filled the allantoid, taking care to ftop his noftnls dur- 

 ing: expiration. The allantoid was filled, in repeated trials, 

 by about 56 expirations, as natural as poffible ; and as its 

 capacity was 2400 cubic inches, the average bulk ot air 

 thrown out of the lungs by each expiration, was 42.8 cubic 

 inches He then fixed another allantoid, whofe capacity 

 had been previoufly afcertained, to the end of the upright 

 tube ; and having filled it with atmofphenc air, he inlpired 

 the air from one allantoid and expired it into the other, and 

 the quantities were found to be nearly the fame. Several 

 perfons cf the middle fize repeated this experiment witl 

 nearly 

 more than 

 experiment 



into a tub ot water up 



tation of the lungs from the afcent and defcent ot the water, 

 he obtained, by feveral trials, nearly the fame refults ; and 

 when thefe fame men were made to breathe from and into 

 the allantoids, in the manner above defcribed, the corre- 

 fpondence by the two methods was almoft complete. (Men- 

 zies on Refpiration, p. 21, et feq.) As there feems no ob- 

 vious fource of inaccuracy in the proceffes here employed, 

 and their refults fo remarkably coincide ; and as they pre- 

 fent the average bulk deduced from 56 refpirations, we may 

 conclude, fays Dr. Bollock, that 40 cubic inches is the 

 quantity of air employed in an ordinary aft of refpiration. 

 Effay on Refpiration, p. 34. Inquiry into the Changes, 



&c. $ 85. 



Mellrs. Allen and Pepys endeavoured to determine the 

 quantity of air received into the lungs in an ordinary infpi- 

 ration : 3460 cubic inches of atmofpheric air were paired 

 through the lungs in 1 1 minutes, by 58 refpirations. As, 

 on ordinary occafions, the perfon breathed 19 times in a mi- 

 nute, it is inferred that, by multiplying the time confumed 

 in the experiment by the number of natural refpirations m a 

 minute, and dividing the whole bulk of air by the produft, 

 we obtain the true bulk of air received into the lungs 

 at each natural infpiration ; thus 11 X 19 = 209; and 

 = 16.5 cubic inches, the quantity of a fingle natural 

 infpiration. (Phil. Tranf. 1808, p. 256.) Mr. Ellis jultly 

 obferves, that not only do the efforts of the mind, and the 

 operations of the apparatus, interfere greatly with the na- 

 tural aaions of the refpiratory organs, but the grofs quan- 

 tity of air received in 58 preternatural infpirations can never 

 with juftice be afl'umed as a true meafure of the quantity 

 breathed in 209 natural refpirations. The experiments of 

 Dr. Menzies therefore ft ill feem the moft unexceptionable 

 on this fubjeft. 



The difficulty in arriving, by 

 conclufions refpedting the volume 

 lungs in each infpiration, may arife 

 ftate or capacity of thofe organs 

 from the relative vigour or debility of the mufcular powers 

 carrying on the refpiratory function ; from the circum- 

 ftances in which the animal is placed ; the compofition of 

 the air itfelf ; or the manner in which it is breathed. In 

 many modes of experiment alfo, the friaion between the 

 1 



temperature, which the air, during its refpiration, fuffers -, 

 from the difficulty of breathing in a natural manner when 

 the mind is directing that procefs ; and from the embarraff- 

 ments oppofed to the natural action of the refpiratory or- 

 gans by the contrivances adapted to them. 



It will not be denied, that the fize and capacity of the 

 cheftmuft, in a certain degree, regulate the quantity of air 

 which is taken into, or expelled from it ; and fince refpi- 

 ration is neither wholly a voluntary nor an involuntary act, 

 but, within certain limits, partakes of the nature of both, 

 and is carried on by the exertion of mufcular powers, the 

 bulk of refpired air muft vary alfo, either from an altera- 

 tion in the action of thefe powers, or from a change in the 

 will of the agent who exerts them. This may be illuftrated 

 by confidering the different quantities of air taken into the 

 luno-s in different ftates of natural and forced refpiration. 

 Dr^ Goodwyn, fuppofing a perfon at death to make a com.- 



experiment, at certain 

 of air taken into the 

 from a difference in the 

 in different individuals ; 



cheft, in fubje&s who had died a natural death by difeafe, 

 previous to which the expiratory powers muft have been 

 much weakened, and unable, in confequence, to expel fo 

 much air as when in a ftate of health and vigour ; and in 

 fuch cafes, therefore, expiration might be final without 

 being complete. Mr. Cruickfhank obferves, accordingly, 

 that the lungs in the dead body, (though expiration is the 

 laft action of life,) always retain more air than is given out 

 at feveral expirations. (On Infenfible Perfpiration, p. 97.) 

 By a very different mode of experiment, we find Mr. Davy 

 to conclude that his lungs, after a forced expiration, contain 

 only 32 cubic inches of air, when it is reduced to the tem- 

 perature of 55 , but which, by the heat of the lungs, and 

 faturation with moifture, are increafed to 41 cubic inches; 

 and, after a natural expiration, they contained 1 18 cubic 

 inches (Refearches, p. 409, 410.) ; fo that the difference 

 between the two ftates of natural and forced expiration is 77, 

 which is fomewhat more than Dr. Menzies allows, who re- 

 marked that many men, after an ordinary expiration, could 

 Itill expel from their lungs 70 cubic inches oi air. (Diff. 

 on Refpiration, p. 31.) Mr. Davy adds, that his ellimate 

 of 118 cubic inches, as the capacity of the lungs after 

 natural expiration, agrees very well with that of Dr. Good- 

 wyn, who makes it about 109; and, on the fuppofition 

 that the general debility which precedes the ordinary ex- 

 tinction of life, fo weakens the expiratory mufcles, as to 

 difable them from making fo complete an expuliion of the 

 air, as they can effect when in health and vigour, the agree- 

 ment is very ftriking ; for nearly the fame quantity of air 

 would, in that cafe, remain in the lungs at the period of 

 natural death, as after that of ordinary expiration. 



Meffrs. Allen and Pepys found that the healthy lungs of 

 a ftout man, five feet ten inches high, contained 108 cubic 

 inches of air after death. Phil. Tranf. 1809, p. 410, et 

 feq. 



Dr. Bollock conceives, that Dr. Goodwyn's eftimate of 

 109 cubic inches of air remaining in the lungs after com- 

 plete expiration, is not very remote from the truth ; and he 

 objefts to Mr. Davy's mode of afcertaining the refidual air 

 of the lungs after a forced expiration, from a fuppofition 

 that the hydrogen gas which "lie infpired for that purpofe 

 was not, in confequence of its low fpecific gravity, uni- 

 formly 



