230 RESPIRATION. 



more firmly, and contains, apparently, more fibrin ; $rd, 

 that it contains more oxygen, less carbonic acid, and 

 perhaps less nitrogen. 



The third difference is, probably, the most important. 

 It might be assumed from what has been said of 

 the changes of the inspired air; and it is proved, by 

 examination of the blood itself. As before remarked 

 however (p. 98), the absolute quantity of carbonic acid is in 

 both arterial and venous blood greater than that of the 

 oxygen, although the amount is relatively less after the 

 blood's passage through the lungs. 



The oxygen absorbed into the blood from the atmospheric 

 air in the lungs is in part simply dissolved, but probably 

 for the most part, combined chemically with the cruorin of 

 the red blood corpuscles. In this condition, it is carried in 

 the arterial blood to the various parts of the body, and 

 with it is, in the capillary system of vessels, brought into 

 near relation or contact with the elementary parts of the 

 tissues. Herein, co-operating probably in the process of 

 nutrition, or in the removal of disintegrated parts of the 

 tissues, a certain portion of the oxygen which the arterial 

 blood contains disappears, and a proportionate quantity of 

 carbonic acid and water is formed. 



But it is not alone in the disintegrating processes to 

 which all parts of the body are liable, that oxygen is con- 

 sumed and carbonic acid and water are formed in its 

 consumption. A like process occurs in the blood itself, 

 independently of the decay of the tissues; for on the 

 continuance of such chemical processes depend, directly 

 or indirectly, not only the temperature of the body, but 

 all the forces, the nervous, the muscular, and others, 

 manifested by the living organism. 



The venous blood, containing the new-formed carbonic 

 acid, returns to the lungs, where a portion of the carbonic 

 acid is exhaled, and a fresh supply of oxygen is again 

 taken in. 



