THE CIRCULATION OF THE BLOOD 



137 



containing a pigment, hemoglobin, which gives the red color 

 to the blood ; and the white corpuscles, which are colorless, 

 nucleated cells. 



Important data on the number, size, and surface area of 

 the corpuscles will be found in connection with Fig. 65. 



3. The white blood corpuscles. The white blood corpuscles 

 really comprise several different kinds of cells, having differ- 

 ent functions, the study and explanation of which belong to 

 advanced rather than to 

 elementary physiology. It 

 is enough for our purpose 

 to state that these cells are 

 not confined to the blood, 

 but work their way out of 

 the blood vessels between 

 the cells of the capillary 

 walls and are often found 

 in the lymph spaces of the 

 tissues as wandering cells. 

 The latter term refers to 

 their movement from place F IG . 66. Amoeboid movement of a white 

 to place. The cytoplasm of corpuscle 



the white Corpuscle is a Showing four consecutive positions among 

 . . , (. . , . . a group of red corpuscles 



thick, viscous fluid without 



constant or definite form. In locomotion the cytoplasm flows 

 slowly from some part of the surface in the direction of 

 motion, forming what is known as a pseudopodium (from the 

 Greek, meaning a false foot), as shown in Fig. 66 ; the rest 

 of the body of the corpuscle then flows into the pseudo- 

 podium. By the continuation of this process the white cor- 

 puscles make their way through the spaces of the connective 

 tissue. Locomotion by means of pseudopodia is frequently 

 spoken of as amoeboid, from the amoeba, a unicellular animal 

 which moves in the same manner. (See Chapter XXIII for 

 examples of the functions of white blood corpuscles.) 



