8 



HUMAN BIOLOGY 



have a characteristic method of locomotion, in the process 

 of which they change their shape ; they can creep along in 

 a direction opposite to that of the blood current, and they 



red corpuscles 

 edge view 



white corpuscles 

 nucleus not seen 



white corpuscles 



nucleus at centre 

 of each 



Fig. 5. — Cells of human blood. 



have even been seen forcing their way through the walls of 

 small blood vessels by pushing out slender processes called 

 false feet. They then wander about in the tissues of the 

 body, and, as we shall soon see, do us great 

 service. The white corpuscles closely re- 

 semble in structure and functions a kind 

 of single-celled animal called the Amoeba 

 (A. B.,>Fig. 12'6). 



The red corpuscles have no power of in- 

 dependent motion. They are circular 

 disks, concave on both surfaces. Some 

 idea of the minute size of these cells may 

 be gained from the fact that ten millions 

 of them would just about cover a space one inch square. 

 There is no nucleus in the red corpuscles ; they are, however, 

 formed from cells having a nucleus. 



• A. B. = " Animal Biology." 



10,000,000 red 

 corpuscles could 

 be enclosed in a 

 single layer with- 

 in this square 

 inch 



Fig. 6. — Number of 

 red corpuscles in a 

 square inch. 



