RESPIRATION. 



Is to vary from -.Vth to -r^th : wlien he received the 

 lame air repeatedly into the lungs, it was found to be di- 

 minifhed as much as r^th of its original bulk. ( Relearches, 

 p. 431 — 435. ) The former experiments, however, alone 

 indicate the effects of natural refpiration, and taking an 

 average of their refults, the amount of the diminution will 

 be about ^„th part of the whole air received into the 

 lungs. 



Mr. Murray of Edinburgh made fome experiments on the 

 alterations produced in the air by natural refpiration, from 

 which he calculates (fur the quantity of air infpired was not 

 meafurcd) that there is a lofs of 6 cubic inches in 265. 

 Syftem of Chemiftry, vol. iv. p. 493, 494. 



Meilrs. Allen and Pepys, whole experiments we (hall 

 prefently allude to, as affording the ftrongeft arguments 

 agsinft a change of volume in the refpired air, in natural 

 breathing, met with a different refult, when the circum- 

 ftances of the experiment were changed. In their four- 

 teenth experiment, 300 cubic inches of atmofpheric air 

 were, in the fpace of three minutes, palled eight or ten 

 times through the lungs, until refpiration became extremely 

 laborious, and the operator was compelled to defilt. On 

 analyfing the refpired air, it was found to contain, in 100 

 parts, only 5.5 oxygen, 9.5 carbonic acid, and 85 parts of 

 nitrogen gas. In the fifteenth experiment, which occupied 

 alfo about three minutes, until the operator became quite 

 infenfible, the fame quantity of air was employed, and af- 

 forded, by analyfis, nearly the fame refults ; for it con- 

 tained, in 100 parts, 4 of oxygen, 10 of carbonic acid, and 

 86 of nitrogen. In the former experiment we obferve, 

 therefore, an increafe of 6 parts of nitrogen, and a lofs of 



6 parts oi oxygen ; and in the latter, the oxygen had loft 



7 from 21, and the nitrogen had gained 7 upon 29. (Phil. 

 Trruif. 1808, p. 260.) Hence it is inferred, that when, as 

 in thefe experiments, refpiration is attended with diftrefiing 

 circumftanccs, there is reafon to conclude that a portion of 

 oxygen is abforbed. Ibid. p. 2 So. 



In fome experiments on the refpiration of rabbits and of 

 guinea pigs, Mr. Berthollet found that the bulk of acid gas 

 produced did not quite equal that of the oxygen which dif- 

 appeared ; fo that the lois of oxygen appeared to vary from 

 1.07 to 4.C9/W cent. 



We proceed to ftate the refult of thofe inquiries, in 

 which the volume of the air has been found not to undergo 

 diminution in the adl of breathing. Among the earlieft ex- 

 periments of Dr. Frieitlev on refpiration is one, in which 

 he confined a rnouic in a jar containing a given quantity of 

 air, which was inverted over mercury. The animal was 

 differed to remain two or three days after he had died, in 

 which time there was no fenfible diminution of the air; but 

 on palling lime-water into the jar, the air was diminifhed 

 h part of its bulk ; and when, in a fublequent experi- 

 ment, the refidual air was agitated in water, it was reduced 

 between one-fifth and one-lixth of the whole. Obf. on Air, 

 vol. v. p. 1 12, et feq. 



Dr. Crawford found, alfo, that when the experiment 

 was made over mercury, the diminution was not fenfible ; 

 but that, if water of potafla was added to the refidual air, 

 it became mild, and the air was diminifhed in the fame de- 

 gree as if the experiment had been made over water, or 

 nearly one-fifth of its bulk. (On Animal Heat, p. 146.) 

 The variations in thefe refults, compared with lliole be- 

 fore enumerated, arifc, no doubt, from the more or K f s 

 complete attraction of the carbonic acid by the fluids, over 

 which the experiments were made ; and, from the whole ol 

 them, we may cwllcct, that when mercury is employed, 

 b has no attraction for carbonic acid, the diminution is 



hardly fenfible ; but that, when this acid is completely ab- 

 llracted by an alkaline fluid, the lofs of bulk amount* 

 nearly to one-fifth oi the whole air employed. This infer- 

 ence correfponds very exactly with what occurs in vegeta- 

 tion, and in the relpiration of the inferior animals. 



In the year 1806, Mr. Dalton's attention was direfted to 

 this fubject, and he fatisfied himfelf, by numerous experi- 

 ments, that the bulk of carbonic acid, formed in refpiration, 

 was exactly equal to that of the oxygen gas conlumed. On 

 repeating thefe experiments, Dr. Thomfon obtained, in 

 fome cafes, nearly the fame refults ; but, upon the whole, 

 the bulk of oxygen that difappeared was fomewhat greater 

 than that of the carbonic acid formed. The difference, 

 however, varied confiderably, and kept pace with the dimi- 

 nution in the whole bulk of air; whence he confiders it to 

 ariie from the abltraftion of a part of the air by fome other 

 way than by refpiration : and if this be allowed for, he be- 

 lieves the bulk of acid produced to be precifely equal to 

 that of oxygen gas loft. Hence, fays he, this oxygen mull 

 he changed into carbonic acid in the lungs ; for oxygen gas, 

 when changed into carbonic acid, does not fenfibly alter its 

 bulk. Syftem of Chemiftry, 3d edition, vol. v. p. 736, 

 and 774. 



Thefe conclufions have been completely confirmed by the 

 very accurate experiments, already noticed, of Allen and 

 Pepys. There was a lofs of 23 cubic inches only in 3460 

 breathed once, at 58 refpirations, which occupied 1 1 mi- 

 nutes. In another experiment, 9890 cubic inches, of which 

 the breathing occupied 245 minutes, loft only l.S. In fub- 

 fequent experiments on the refpiration of a guinea pig, thefe 

 chemifts found, that when 310 cubic inches of atmofpheric 

 air were breathed for 25 minutes by this animal, its volume 

 experienced no variation whatever ; and the portion of its 

 oxygen, which difappeared, was replaced by an equal bulk 

 of carbonic acid. Thefe refults were particularly iatisfac- 

 tory in their tendency to eftablifh the point, that the air un- 

 dergoes no diminution ; becaufe the time which they oc- 

 cupied was more confiderable, and the chance of error, 

 therefore, diminifhed. The third trial with the guinea pig 

 occupied one hour: the bulk of the atmofpheric air, before 

 the experiment, was 1060 cubic inches ; after the experi- 

 ment, 1061 ; the carbonic acid formed 53 cubic inches ; 

 the carbonic acid per minute, .88 of a cubic inch. (Phil. 

 Tranf. 1809, p. 414.) Wherefore they juitly conclude, 

 that when atmofpheric air alone is refpired, no other change 

 is produced in it than the fiibllitution of a certain portion 

 of carbonic acid gas for an equal volume of oxygen. 



The refults of all the trials made by thefe gentlemen were 

 not uniform, and the deficiency was fometimes greater than 

 what lias bi en ftatcd. The deficiency varied from 4 to 62 

 cubic inches in ten experiments ; in each of which, between 

 3 and 4000 cubic inches of air were breathed once, the time 

 employed being 10 or ii minutes in each experiment. 

 'I'll y confider that the deficiency principally arifes from the 

 lall expiration being made into a gafometer, and confe- 

 ig witli more refiftance ; fo that tin- lungs are 

 lefs completely evacuated than in the expiration into the 

 open air, with which the experiment commenced. 



The difficulty, which thefe gentlemen allude to, oi bring- 

 in:; the lunge to the fame ftate exactly at the end aa they 



Uiiv in at the beginning of the experiment, is evinced by 



the refult of tli il til rti enth trial, which alio affords a ftrong 

 argument againll the diminution of hulk, winch has hitherto 

 been almofi generally aflu refull oi the refpiratory 



procefs. In 5^ minutes, 3300 cubic inches were infpired, 

 and 33 1 1 expired ; thus 1 an increafe oi 11. 



Amid this conflict of authorities, we have no difficult] 



in 



