142 



ON THE CIRCULATION OF THE BLOOD, 



son respires 48,000 cubic inches in an hour, or 1,152,000 cubic inches in the 

 course of a day ; a quantity equal to about 79 hogsheads. 



A similar train of experiments has more lately been pursued by Messrs. 

 Allen and Pepys, and will be found fully detailed in the Transactions of the 

 Royal Society for 1808. They confirm the preceding proportions, excepting 

 in the retention of nitrogen ; this substance having been found by Messrs. 

 Allen and Pepys to have been returned in every respiration, in the precise 

 proportion in which it was received. It is highly probable, however, that the 

 diet of these two sets of ingenious experimenters had not previously con- 

 sisted of the same proportion of animal and vegetable materials ; and that the 

 blood in the former instance was less charged with nitrogen than in the 

 latter ; which would at once account for the difference. 



Upon Sir Humphry Davy's experiments, however, the quantity of nitro- 

 gen received by the lungs is very inconsiderable, not amounting to more 

 than two-tenths of a cubic inch in an inspiration. And omitting the con- 

 sideration of this gas, as also that of caloric, on account of the unsettled state 

 of the question, respiration, from this view of the subject, consists merely in 

 the act of receiving oxygen, and throwing out carbonic acid gas ; the lungs 

 imbibing and communicating to the system not less than 32.4 cubic inches of 

 the former, and parting with not less than 26.5 of the latter, every minute. 

 So that, taking the gravity of carbonic acid gas, as calculated by Lavoisier, 

 eleven ounces of solid carbon or charcoal are emitted from the lungs every 

 twenty-four hours.* 



The whole of the theory and some of the supposed facts here advanced, 

 however, have of late been very considerably disputed by Mr. Ellis, in his 

 Inquiry into the Changes induced on Atmospheric Air by the Germination of 

 Seeds. He concurs with Messrs. Allen and Pepys, in ascertaining that pre- 

 cisely the same quantity of nitrogen is expired as is inspired ; but he objects 

 to their conclusion, that the whole of any constituent element of respired air 

 introduced into the air-vesicles, and not returned by the alternate expiration, 

 is necessarily conveyed into the blood-vessels, believing that much of this 

 may remain unascertained, in consequence of an increased, but not sensibly 

 increased, expansion of the chest. He admits that carbonic vapour is thrown 

 forth in the quantity usually alleged, with every act of expiration ; but he 

 offers evidence to prove that it is the carbon only that is discharged from 

 the animal system, in connexion with the exhaling vapour ; contending that 

 the carbon thus existing is separated from the vapour by its union TsDith the 

 whole of the oxygen introduced by the previous act of inspiration, by which 

 alone it is converted into carbonic acid gas : for he found the same decom- 

 position of atmospheric air produced by introducing a small bladder, moistened, 

 and filled with any substance, or perfectly empty, and introduced into an 

 inverted glass containing a certain proportion of atmospheric air, standing 

 upon quicksilver. He denies, therefore, that the air-vessels are in any de- 

 gree porous to gases of any kind, excepting caloric ; and, consequently, 

 denies that the blood is converted from a deep modena hue into a bright 

 scarlet by its union with oxygen ; believing, or seeming to believe, that this 

 result is entirely produced by the action of the caloric separated in the air- 

 vesicles upon the union of the carbon of the vapour exhaled from their sur- 

 faces, with the oxygen introduced by inspiration. So that, according to this 

 theory, respiration is nothing more than an introduction of caloric into the 

 system, and the conversion of a portion of oxygen (the whole received by the 

 act of inspiration) into an equal bulk of carbonic acid by the carbon exhaled 

 from the living organized body. Air, therefore, examined after respiration, 

 is found to differ from the same air before it is breathed, in having lost a por- 

 tion of oxygen, gained an equal volume of carbonic acid, and in being loaded 

 with pure watery vapour, the vapour thrown off from the lungs ; and he 

 has offered an additional proof that the oxygen of the carbonic acid is that 

 introduced in the act of inspiration, by showing, as in the case of breath- 



* PWl. Trans. 1808, part ii. 249. 



