THEORY OF RESPIRATION. 85 



ctently acquainted with the fubje6l to be able to explain the 



procefs. But we can fee at leaft, that carbon and h)'drogen ufe of refplra- 



muft be abftraaed from that part of the chyle which is to be ^'""J" that con- 



converted into fibrina, and we know that theie fubitances are 



afiually thrown out in refpiration. We may conclude then 



that one ufe of the air ablorbed is to abflrafl a quantity of 



carbon and hydrogen from a part of the chyle by compound 



affinity, in fuch a manner that the remainder becomes fibrina : 



Therefore one end of refpiration is to form fibrina. 



It appears then, from the above-mentioned fa6ls, that the tife cannot fub- 

 perfedion of tiie blood is almoft totally dependent on refpi. ^^ without it. 

 ration; whenever therefore this fun6!ion is fufpended but for 

 a very fliort time, death is the confequence. 



It is well known that all the more perfe6l animals poffefs a The elevated 

 teujperature confiderabiy higher than the furrouoding atmo- [^^^^J^^P^j.^^^ 

 fphere ; the caufe however of this increafed temperature, re- animals is caufed 

 mained unexplained for a confiderabie time. At length Dr. [j^^^'^/J^o^^^^^^ 

 Black's theory of latent heat became known, when feveral fation of air. 

 attempts were made to explain the caufe of the increafe of 

 temperature, or flandard heat of the body, but none of them 

 were fatisfactory. Dr, Thomfon has however given us the 

 following ingenious theory ; As the air is abforbed unaltered 

 by the blood, it is evident that it will give out the greateft 

 portion of its caloric during circulation ; that portion therefore 

 which is emitted at the inftant that the air combines with the 

 blood, is united to the carbonic acid, converting it into the 

 {late of gas, and the water into vapour. It appears more- 

 over, that the heat of the blood is fomewhat raifed during 

 circulation ; for Mr. John Hunter found that the blood iri the 

 heart was a degree higher than in any other part of the body. 



From the fads which have now been alluded to, it appears Recapitulation, 

 that the following changes are produced by refpiration ; The 

 blood is propelled, by the conlradlion of the heart, into the 

 pulmonary artery, which, by its numerous ramifications, con- 

 veys the blood into the fmall branches of the air-cells of the 

 lungs, which are of fo fine a texture as to admit the abforptior) 

 of a portion of air. The blood having undergone this altera- 

 tion, is returned into the heart by the pulmonary veins, from 

 whence it is circulated over the whole body. During the cir- 

 culation, the air which has been abforbed undergoes a gradual 

 idecompofition ; carbonic acid and water are formed, which, 



together 



