

THE BLOOD 157 



globin is the essential part of the red corpuscle. It con- 

 tains a small amount of iron, which gives to it the prop- 

 erty of carrying oxygen without itself being oxidized. By 

 means of the hemoglobin the red corpuscles are able to 

 carry oxygen from the lungs to all parts of the body. 

 When the hemoglobin contains a large amount of oxy- 

 gen the blood is of a bright red color, but as the oxygen 

 is used up it becomes darker, or almost purple. Bright 

 red blood, called arterial blood, is continually flowing 

 toward the cells of the body; while that returning from 

 the cells, called venous blood, is purple in color, from the 

 lack of oxygen. 



275. White corpuscles. White corpuscles are each 

 about ^0^0 of an inch in diameter, and are about -- as 

 numerous as the red corpuscles. 

 They are round and colorless, and 

 each contains a nucleus. They 

 have the power of changing their 

 shape, and of adhering to the 

 sides of a blood tube, and of 

 passing through its wall, and of 

 moving about between the cells 



.. i j , , , i A white blood cell of a frog, 



of the body as though endowed sketc hed at intervals of two 

 with a will of their own. They <> r three minutes, showing its 



changes in form (X 300). 



have important duties to perform 



in destroying disease germs and other foreign substances, 

 and in the healing of wounds. (See p. 398.) 

 ^ 276. Plasma. The liquid part of the blood is called 

 the plasma. It is composed of ninetyparts of water, 

 holding in solution about eight parts of aTrJumin and two 

 parts of mineral matter. The mineral matter is mostly soda 

 and potash. This alkaline property of the blood plasma 

 aids it in dissolving carbonic acid gas, and in carrying it to 



