RESPIRATION. 



of refpired air, fays profeffor Pfaff, depends not only on 

 the time during which a given volume of air is refpired, but 

 principally on the magnitude of the volume of air itfelf ; it 

 mult be proportionally lefs the greater the quantity mfpired. 

 He breathed 144 cubic inches of air once only in the time 

 of ten or twelve feconds, and the diminution was four cubic 

 inches, or -,-^th of the primitive volume ; when he refpired 

 the fame volume of air twice, during twenty feconds, it loft 

 eight cubic inches, or ^th ; and when it was thrice Vefpired, 

 during thirty feconds, the diminution amounted to twelve 

 cubic inches, or -rVth of the primitive volume. (Nichol- 

 fon's Journal, December 1805.) Now, in all thefe cafes, 

 the volume of air refpired was precifely the fame, and could 

 not, therefore, affeft the ratio of diminution : but as the 

 times were doubled and tripled, fo nearly were the degrees 

 of diminution. But the more frequently the fame air is 

 breathed, the more unfit does it become for refpiration ; 

 and to this change of compolition, more than to the time, 

 or the magnitude of the volume of air., is the increafed de- 

 gree of diminution to be afcribed. 



This will perhaps appear more drifting, if we attend to 

 what happens in refpiring nitrous oxyd, which is compofed 

 of the lame elements as atmofpheric air, but contains a 

 much larger proportion of oxygen. After exhaufting his 

 lungs, Mr. Davy mfpired 108 cubic inches of this gas, 

 which, when expired, were reduced to 99, or had loft T vth 

 of their bulk. When he made two refpirations of the 

 fame quantity of the oxyd, the diminution was to 95, or 

 about |th ; and when he refpired 102 cubic inches of nitrous 

 oxyd, mixed with T Vth of common air, for half a minute, 

 the volume of air, after the feventh expiration, was reduced 

 to 62, or had fuffered a lofs equal to ,. J. r . ( Researches, 

 pp. 394. 416.) Hence it appears, that in the natural re- 

 spiration of atmofpheric air, only a fmall diminution of its 

 bulk takes place : that this diminution increafes as the air 

 becomes vitiated by repeated refpirations, or is breathed in 

 a preternatural manner : and that when a gas of the fame 

 elementary materials, but combined in very different pro- 

 portions, is fubftituted into the place of pure atmofpheric 

 air, the diminution increafes in a tenfold degree. Now 

 the repeated breathing of the fame atmofpheric air' 

 has been ihewn to bring on the moft diftrefsful fymp. 

 toms, and at length an utter inability to continue refpira- 

 tion ; and Mr. Davy tells us, that after a voluntary ex- 

 haustion ot his lungs, he could refpire the nitrous oxyd 

 with accuracy, when ftooping, for about half a minute, but, 

 even then, ltrong fenfations were produced, with fulnefs 

 about the head rather alarming : that if the refpiration ex- 

 tended to three-fourths of a minute, he could not rely on the 

 accuracy of any experiment ; and that the determination of 

 blood to the head became, in lefs than a minute, fo great 

 as often to deprive him of voluntary power over the rnuf- 

 cles of his mouth. (Refearches, p. 392.) But refpira- 

 tion is a function carried on by the exertion of mufcuhy- 

 powers, in a great degree obedient to the will ; and the 

 quantity of refidual air in the lungs in preternatural refpira- 

 tion will at all times be much influenced by the manner in 

 whieh the will exerts itfelf, and the degree in which the 

 rnufcles are able to ad. When, therefore, the power of 

 the will over the rnufcles is in any degree dimimfhed, or is 

 wholly lolt, or the rnufcles themfelves are much weakened, 

 a proportional derangement will take place in the refpira- 

 tory tundhon ; and as, in the natural condition of the body, 

 expiration is fubfequent to infpiration, the ability to in. 

 fpire will laft longer than the ability to expire : confequently 

 the ceffation of the procefs is brought about by a failure 

 m the expiratory powers. But if the expiratory powers 



are unable to expel the air from the lungs, it mult remain 

 in thofe organs ; and hence we fee in all the foregoino- ex- 

 amples, that the diminution in the volume of expired air 

 was greater in proportion as the refpiratory organs fuffered 

 diftrefs or oppreffion, and amounted even to more than one- 

 third of the air inlpired, when all voluntary powers ceafed 

 Inquiry, &c. § 86 — 92. 



From the above data it may be efthnated, that by each 

 ordinary expiration one-feventh part of the whole contents 

 of the lungs is dilcharged, and that by the molt violent 

 expiration tomewhat more than four-fevenths of the air con 

 tamed in them is evacuated. Suppohng that each refpira 

 tion occupies about three feconds, a bulk of air nearly 

 equal to three times the whole contents of the lungs will 

 be expelled ma minute, or about 41 14 times their bulk in 

 24 hours rhe quantity of air refpired during the diurnal 

 period will be 1,152,000 cubic inches, or 666A cubic feet 



U. Changes produced in the Air Although the anciea^s 



were not unacquainted with the general fact, that refpira 

 tion produces a change in the air received into the lunsrs 



n. Iu aCC l Uratc n ° ti0nS rcf P^ in S this change, were fur! 

 ruffled by the experiments of Boyle. He not only proved 

 by means of the air-pump, the abfolute necefhty of air to 

 the lupport of animal life, but he farther difcovered that 

 the action of the lungs is quickly fufpended, unlefs they 

 are furmlhed with a regular fupply of frefh air. (Works 

 v. 1. p. 99, et feq.) « Animals, whofe hearts have two 

 ventricles, and no foramen ovale," fays Mr. Derham, « as 

 birds, dogs, cats, and mice, die under the action of the 

 air-pump ,„ lefs than half a minute, counting from the 

 very hrft exfuClion, particularly in a finall receiver " , Phv 

 fico-Theology, p. 8.) The fame pofition is corroborated 

 by an experiment, exhibited before the Royal Society by 

 Dr. Hooke He cut away the ribs, diaphragm, and peri- 

 cardium of a dog, whereby the lungs and heart were 

 brought into view; and then dividing the windpipe, he in- 

 troduced into it the nozzle of a pair of double bellows, and 

 made, at the fame time, feveral imall punctures through the 

 outer coat of the lungs. By blowing in a ft ream of frefh 

 air which continued to efcape through the fmall apertures 



fi,H ^ 'aa S I' f "" enaWed l ° kee P thole organs 

 fully diftended. A. long as he fupplied the lungs with 

 air, the actions of life continued, and the heart beat very 

 regularly ; but, on intermitting the fupply, the dog would 

 immediately faff mto dying convulfive fits ; and revive aaain 

 as foon as the lungs were filled with a ftream of frefti°air 



Sfr Zi TT t 5 r ° U f5 h r H I L Un S S «»ti™d both during 

 their diftended and collapfe4 ftate, and as well when the? 

 were kept at reft, as during their ftate of motion; whence 

 he concluded, that neither the motion of the lungs, nor the 

 reflation of their motion, nor the (topping of the cir- 

 culation of the blood through them, was the immediate 

 caufe of death; but the want of a fufficient fupply 

 ot frefh air. Lowthorp's Abridg. Phil. Tranf. v / 

 p. 66. ' 3' 



From thefe fafts it was naturally concluded, that the air 

 had undergone fome important change during its continuance 

 in the pulmonary vel.cles, and a variety of hypothefes and 

 conjectures were formed to account for this alteration. 

 The knowledge which was then obtained refpeding the air 

 was, however, almoft entirely confined to its mechanical 

 properties, fo tnat the theories of refpiration, formed dur 

 mg this period, were neceflarily crude and imperfeft 

 Boyle perceived that the a,r, in faffing through the luW 

 became loaded with a quantity of aqueous vapour, and 1,e 

 farther fuppofed, that it acquired, what he calls, recremen- 

 tuious fteams (Works, v. 3. p. 37 ,, et feq>) . but re . 



fpecting 



