CHAP, vi.] OF LIVING LIQUIDS. 69 



The blood is then called arterial: thereupon the globules are 

 conveyed with their provision of oxygen into the circulatory 

 apparatus. Soon they find their way to the finest vessels of 

 this system, where they are almost in contact with the anatomical 

 elements of the tissues. Between the globules and the anatom- 

 ical elements an exchange of gas is there accomplished which is 

 one of the primordial acts of nutrition. 



In effect, the vital condition by excellence for every anatom- 

 ical element is to be oxydized, more or less slowly. But this 

 process of oxydation produces, along with other chemical com- 

 pounds, carbonic acid gas, which, if it was not eliminated in the 

 degree of its formation, would soon bring death to the anatomical 

 element. The function of the red globules of the blood is pre- 

 cisely to take back that carbonic acid, and to furnish in exchange 

 their vivifying oxygen. 



The visible sign of this gaseous exchange is the change of 

 coloration of the globule, which becomes blackish when it has 

 parted with its oxygen to charge itself with carbonic acid. This 

 black or venous blood contains much less oxygen than the arterial 

 blood. According to Magnus, there is in the arterial blood 

 38 of oxygen to 100 of carbonic acid, and the proportion is only 

 22 to 100 in the venous blood. The venous blood is blood im- 

 poverished by nutrition ; it contains fewer globules, less fibrine, 

 and on the contrary more salts, a certain number of which are 

 nutritive residua. 1 



Every anatomical element transforms oxygen into carbonic 

 acid by the mere agency of nutrition ; but it consumes a much 

 greater quantity when it exercises a special function, and then 

 the absorption of oxygen is rigorously in proportion to the 

 degree of activity of the chemical element. For instance, if 

 we cut all the veins which are distributed to a muscle, all volun- 

 tary contraction becoming for it now impossible, the arterial 

 blood traverses it, losing only a small part of its oxygen, and 

 it is red when it passes into the veins (Ch. Bernard). But if 

 1 Longet, TraiU de Physiologic, t. I., p. 581. 



