CHEMICAL EFFECTS OF RESPIRATION. 337 



open air : so admirably have the faculties of 

 animals been, in every instance, accommodated 

 to their respective wants. 



Since carbonic acid consists of oxygen and 

 carbon, it is evident that the portion of that gas 

 which is exhaled from the lungs is the result of 

 the combination of either the whole, or a part, 

 of the oxygen gas, which has disappeared during 

 the act of respiration, with the carbon contained 

 in the dark venous blood, which is brought to 

 the lungs. The blood having thus parted with 

 its superabundant carbon, which escapes in the 

 form of carbonic acid gas, regains its natural Ver- 

 million colour, and is now qualified to be again 

 transmitted to the different parts of the body for 

 their nourishment and growth. As the blood 

 contains a greater proportion of carbon than the 

 animal solids and fluids which are formed from 

 it, this superabundant carbon gradually accu- 

 mulates in proportion as its other principles, 

 (namely, oxygen, hydrogen, and nitrogen) are 

 abstracted from it by the processes of secretion 

 and nutrition. By the time it has returned to 

 the heart, therefore, it is loaded with carbon, 

 a principle, which, when in excess, becomes 

 noxious, and requires to be removed from the 

 blood, by combining it with a fresh quantity of 

 oxygen obtained from the atmosphere. It is not 

 yet satisfactorily determined whether the whole 



VOL. II. z 



