RESPIRATION. 



of which do not even breathe, that is, do not receive and 

 emit air at all. In confequence of the medium in which 

 fifties are immerfed, they cannot take in the atmofphcric air 

 in its elaftic ftate, and they confequently have an apparatus, 

 altogether different from that which exilts in the three 

 claffes already named, for the purpofe of producing analo- 

 gous effects in then- economy. They are furnifhed with a 

 paffage communicating with the fauces or cefophagus, and 

 terminating in the external furface of the body, through 

 which a part of the water received into the mouth is forci- 

 bly propelled. In this paffage, the branchiae or gills are 

 fituated ; and the blood, which circulates in their (ringed 

 extremities, is thus expofed to the aftion of a quantity of 

 air, which the water always holds in folution. Cruitaceous 

 animals, and many of the mollufca, have organs more or 

 lefs fimilar in ilructure and functions to the gills of fifties. 

 InfeCls, both in their larva and perfeft Hates, poffefs nume- 

 rous ramitied tubes, diltnbuted over their whole body, and 

 provided with open mouths, which admit the paflage to and 

 fro of the external air. Although the ftru&ure of the or- 

 gans in fifties and infe£ts is fo different from that which we 

 find in mammalia, birds, and reptiles, they perform an ana- 

 logous office, anfwer the fame general purpofes in the ani- 

 m.d economy, and are confidered equally in the light of 

 organs of refpiration ; this term being employed now to de- 

 note the general effect produced by thefe various organiza- 

 tions, without any reference to the means through which 

 it is produced ; although it was originally applied to the 

 paffage of the air to and from the lungs, when the relults 

 of that procefs were unknown. 



Is refpiration, confidered in its moll extenfive fenfe, a 

 function neceffary to the exiftenee of all animals ? The re- 

 fults of all the inveltigations hitherto made, induce us to 

 anfwer this quellion in the affirmative ; but the point is not 

 yet demontlrated in all cales. 



In Cuvier's clafs of zoophytes, excepting the echinodcr- 

 mata, no refpiratory apparatus has been found ; nor has any 

 been yet difcovered in the inteflinal worms, or in fome of 

 the external worms, as the leech, earth-worm, and others. 

 It may be doubted, fince the analogy on which we ground 

 our opinion of the neceffity of air to animal exiftenee is fo 

 very ftrong, whether the apparent exception afforded by the 

 animals juft enumerated may not arife from our imperfedl 

 knowledge of their organization, and whether more accu- 

 rate inquiries may not either difclofe to us in thefe cafes 

 fome particular organ of refpiration, or fhew us that the 

 function is performed by the external furface of the body 

 in general. We know, in fa£t, by direct experiment, that 

 fome of thefe animals produce changes in the air, and can- 

 not live when debarred from its accefs. 



Tii differences which animals exhibit in their mode of 

 breathing, or in the manner of effecting the changes which 

 their nutritive fluid undergoes from the action of the atmo- 

 fphere, depend on other circumllances in their organization, 

 tables, and animals which have no circulation, refpire 

 by their whole furface, or by means of veffels, which con- 

 vey air to all points of their interior. Thofe only which 

 have a true circulation breathe by a particular organ. The 

 heart being in them a common point of departure and return 

 fur the blood, the vcilcls containing that fluid could calily 

 be fo arranged as to convey it to the lunge, after it had cir- 

 culated through the body : this was obvioufly impractica- 

 ble in inftances, when the nutritive fluid is every where uni- 

 formly expanded, without being contained in veilels. Hence 

 i fpiration by lungs or gills is a function dependent on that 

 of circulation, and may be regarded as a remote confequence 

 tif thofe faculties which charaderife animals. 



Refpiration prefents to our obfervation two very different 

 kinds of phenomena: lit, the motions of the lung?, gills, 

 or other instruments of breathing, or of parts connected 

 with them, by which the former are alternately dilated and 

 contracted for the admiffion and expullion of air, and the 

 latter are expofed to a current of water ; and 2dly, the 

 changes produced in the blood or other animal fluids, and 

 in the air or water, in confequence of their mutual cxpofure 

 in thefe organs. The firlt may be termed the mechanical, 

 and the fecond the chemical phenomena of refpiration. The 

 former, including all the modifications which breathing un- 

 dergoes in laughing, crying, and fighing, in coughing, fneez- 

 ing, hiccoughing, in (training or holding the breath, &c. 

 have been fully confidered under the article LuNG ; in which 

 the anatomy of the organs of refpiration in man is alfo fully 

 detailed. In the articles Mammalia, Bums, Fishes, Rep- 

 tiles, Insects, and Vermes, the breathing organs, and 

 their mechanical phenomena in animals, are confidered. The 

 chemical phenomena are the object of the prefent article. 



The fun&ions of the refpiratory organs are clofely con- 

 nected with the other great proceffes of the animal economy. 

 The heart, brain, and lungs, more particularly influence each 

 other, and prefent, in their mutual relations, numerous and 

 highly interelling coniiderations for the phyiiologift. On 

 thefe points we refer to Heakt, Lungs, and NERVOUS 

 Syjhm. 



In the following article we fliall fpeak, lit, of the quan- 

 tity of air received into the chell ; 2dly, of the changes 

 which this undergoes in breathing, as they have been made 

 out by rcfearches on the refpiration of man and the mam- 

 malia ; 3dly, of the changes produced in the blood ; 4thly, 

 of the various explanations of the mode in which thefe 

 changes are produced ; 5thly, of the refpiration of the dif- 

 ferent gafes ; 6thly, of the chemical phenomena of refpira- 

 tion in other animals, and 7thly, of animal heat. 



I. Number of Refpirations, and Quantity of Air nfpired. — 

 " It appears," fays Dr. Thomfon (Syllem of Chemiltry, 

 v. 5. p. 732.), "that the number of relpir.itions made in a 

 given time differs confiderably in different men. Dr. Hale; 

 reckons them at 20 in a minute. A man, on whom Dr. 

 Menzies made experiments, breathed only 14 times in a 

 minute. Mr. Davy informs us that he breathes between 26 

 and 27 times in a minute. I mylelf make about 19 refpi- 

 rations at an average. The average ot all is 20. Now 20 

 in a minute make 28,800 in 24 hours." 



In his " Inquiry," p. 102, et feq. Mr. Ellis has brought 

 together, from the moft authentic fources, a itatement of 

 the fadts hitherto collected concerning the quantity of air 

 ordinarily infpired. To afcertain this point, many modes 

 of experiment have been adopted, and the c'onclufiona 

 which have been drawn from them very widely differ. 

 Borelli ellimated the bulk of air taken in at a (ingle inspira- 

 tion at 15 cubic inches (de Mot. Animal.) ; Mr. Kite from 

 12 to 17 (Effay on Apparent Death, p. 24.) ; Dr. Goodwyn 

 at 14 (Connection of Life with Refpiration, p. 28, ct feq. ) ; 

 Mr. Davy from 13 to 17 ( Rcfearches, p. 410 and 43 j. ) ; 

 and Drs. .luriiie, Hales, Mailer, and Sauvagcs, at 4c cubic 

 inches. With the conclulion of thefe latter authors the ex- 

 periments of Dr. Menzies nearrj coincide, and as the me- 

 thods which he adopted feem lefs liable to objection than 

 thofe of any Other author, it may not be improper Ihortly 

 to give the detail of tbem, He procured 111 allantoid, and 

 fixed to it a machine confiding of two | large tube , 



joined at right angles nearly in the form "I :i common brafs 



One end ot the horizqntal tube was connected with 



the all.uitoid, and the other received into the mouth, while 



the upright tube, which rofe from its centre, i □mmu.nicated, 



F * 



