Chap. IX] VASCULAR SYSTEM 143 



but merely of a reddish yellow tinge, or yellowish green in venous 

 blood. It is only when great numbers of them are gathered 

 together that a distinct red color is produced. 



Authorities differ regarding the structure of the red corpuscles. 

 Some describe them as consisting of a colorless filmy, elastic frame- 

 work infiltrated in all parts by a red coloring matter termed 

 haemoglobin, which contains a small amount of iron. Others 

 describe them as consisting of a colorless elastic envelope enclosing 

 a solution of haemoglobin. In either case it is correct to consider 

 them as packets of haemoglobin moving passively at the mercy of 

 the blood current. They have no nuclei, are soft, flexible, and 

 elastic, so that they readily Squeeze through apertures and passages 

 narrower than their own diameters, and immediately resume their 

 proper shape. 



Function of the red corpuscles. — The red corpuscles, or eryth- 

 rocytes, by virtue of the haemoglobin which they contain, are 

 emphatically oxygen carriers. Exposed to the air in the lungs the 

 heemoglobin becomes fully charged with detachable oxygen and 

 is known as oxyhsemoglobin. The red corpuscles carry this 

 oxyhsemoglobin to the tissues, where it gives up the loosely en- 

 gaged oxygen. It is then known as reduced haemoglobin and is 

 ready to be carried to the lungs for a fresh supply. The color of 

 the blood is dependent upon this combination of the haemoglobin 

 with oxygen ; when the haemoglobin has its full complement of 

 ox^'gen, the blood has a bright red hue ; when the amount is de- 

 creased, it changes to a dark crimson hue. The scarlet blood is 

 usually found in the arteries, and is called arterial; the dark 

 crimson in the veins, and is called venous blood. 



Life cycle of the red corpuscles. — There is every reason to 

 believe that the red corpuscles, like all the cells of the body, have a 

 definite term of existence, then disintegrate and are replaced by 

 other corpuscles. They originate in the red marrow of the bones, 

 but in case of special need, as after the loss of a large number by 

 hemorrhage, they can be formed in other organs, especially the 

 spleen. Before being forced into the blood stream they lose their 

 nuclei, and this suggests that they do not live a great while in the 

 circulation. Red corpuscles in various stages of disintegration 

 have been found in the substance of the spleen and lymph nodes. 

 Some authorities consider that their destruction takes place in 



