THE BLOOD 



377 



378. The Blood. The blood consists of two parts. 

 One is a colorless liquid called the plasma; the other is a 

 multitude of tiny bodies called corpuscles (cf. 341). 

 The plasma is made up of water and of dissolved mate- 

 rials. Among the dissolved materials are the blood 

 proteids, made out of the proteids digested by the body 

 (cf. 369). There are also fats, dextrose, salt, etc. 

 Besides the foods and minerals, the plasma contains 

 waste substances, chiefly carbon dioxide and urea. 



The corpuscles (Fig. 286) are of 2 kinds, red and white. 

 The red corpuscles are much more numerous than the 

 white ones, but smaller. 

 As seen under the micro- 

 scope, a red corpuscle is 

 a thin, yellow cell (not 

 red), disc-like in shape. 

 The red corpuscles are 

 generally in groups, like 

 "stacks" of coins. The 

 groups appear red. Red 

 corpuscles contain protoplasm and a dark-red substance 

 called hemoglobin (from haima, "blood," and globe). 

 Hemoglobin forms a bright-red compound with oxygen; 

 this is oxyhemoglobin. It is as a part of this compound 

 that oxygen is carried from the lungs to the cells. Bright- 

 red blood is, therefore, blood with a good supply of oxy- 

 gen; dark-red blood is poor in oxygen. 



White corpuscles are also single cells. Like amebas 

 (cf. 333), they have the power of changing their shapes 

 and of moving about. They can pass through the walls 

 of capillaries into the lymph (cf. 379). White corpuscles 



Red 



FIG. 286. 



Blood Corpuscles, White and Red, greatly mag- 

 nified. 



