188 UNCONSCIOUS NERVOUS OPERATIONS 



between the bright arterial blood in the arteries and the 

 dark venous blood of the veins of the systemic circulation. 

 Chemical analysis shows that this difference in the blood 

 corresponds to the difference between the air inspired and 

 the air expired. The immense amount of capillary sur- 

 face which the air reaches in the air cells of the lungs has 

 taken from it a large amount of oxygen and has given up 

 to it carbon dioxide and organic waste, together with 

 some of the water in the venous blood of the capillaries. 

 That is, the blood has been arterialized in the lungs, for 

 (except in the pulmonary circulation, where the reverse is 

 the case) the arteries convey the oxygenated, or purified, 

 nourishing blood, while the veins are filled with the im- 

 pure, partly deoxidized, and poisonous blood. In health 

 both arterial and venous blood contain both oxygen and 

 carbon dioxide, the proportion of oxygen being much 

 larger in the arterialized blood. 



268. Function of the Red Corpuscles. It was stated in 

 the chapter on the Blood that the special function of the 

 red corpuscles is to take up and hold for a time a certain 

 amount of oxygen, and then to give it up to other tissues. 

 The red corpuscles, as we have seen, are chiefly made up 

 of a red substance called hemoglobin, and hemoglobin 

 which has absorbed a considerable amount of oxygen 

 becomes oxy 'hemoglobin, which is of a bright scarlet color. 

 Oxyhemoglobin becomes hemoglobin again and of a dark 

 purplish red when it is deprived of its oxygen. When 

 brought into contact with air in the lungs, the red cor- 

 puscles take up oxygen, while carbon dioxide is given 

 up in return. The oxygen is held b}^ the red corpuscles 

 in loose combination, that is, in such a chemical union 

 as is easily disturbed, the oxygen being readily given up 

 to form other combinations. 



