"RESPIRATION. 617 



into the lungs at each inspiration be accurate, it will follow, that 

 in twenty-four hours 8957*76 cubic inches of oxygen gas are 

 converted into carbonic acid gas by the respiration of every adult, 

 but 8957*76 cubic inches of carbonic|acid weigh 4234 grains, 

 and contain 1155 grains, or very nearly one-sixth of a pound 

 avoirdupois, or two ounces and two-thirds of carbon. This, then, 

 is the amount of carbon discharged^every twenty-four hours from 

 the body by means of the lungs. 



If we reckon the quantity of blood in the body of an adult 

 twenty-six pounds, and that dry blood amounts to twenty per 

 cent of liquid blood, it is obvious that, if the carbonic acid were 

 derived from the carbon of blood (constituting 51*96 of dry 

 blood,) the whole carbon would be consumed in little more than 

 sixteen days. 



5. The general opinion at present entertained is, that the vo- 

 lume of oxygen gas which disappears is greater than that of 

 the carbonic acid gas, which replaces it. If, as is most pro- 

 bable, the oxygen gas is absorbed by the blood in the lungs, and 

 combining with carbon during the circulation, and is evolved in the 

 state of carbonic acid gas when the blood passes next through 

 the lungs, it is at least possible that a portion of the oxygen gas 

 absorbed may combine with hydrogen during the circulation and 

 form water. The experiments of Despretz, which will be stated 

 afterwards, lead to the conclusion that about T l a th of the oxy- 

 gen gas absorbed combines with hydrogen and forms water, and 

 that T 9 (jths of it go to the formation of carbonic acid gas. If 

 this estimate be true we must, tjn order to get the true volume 

 of oxygen gas abstracted from air during respiration, augment 

 the volume of carbonic acid gas evolved by ^th. This would 

 make the average quantity of oxygen abstracted from the air in- 

 spired amount to 4-092 per cent. 



When venous blood passes through the lungs it becomes ar- 

 terial blood, distinguished by its bright scarlet colour. Now, as 

 the colouring matter of blood is the red globules, it is obvious 

 that they must be the portion of the blood which has absorbed 

 oxygen. The blood continues arterial till it passes through the 

 capillary vessels. Here it loses its scarlet colour and becomes 

 venous blood. In the capillaries, therefore, the oxygen which 

 has combined with the globules must be converted into carbonic 



