io6 THE FROG chap. 



on the left, and so on. As a matter of fact, as long as the 

 blood is quite fresh, the leucocytes are in constant movement, 

 sending out and withdrawing little processes of their substance 

 called pseudopods or " false feet," by means of which they 

 can crawl slowly along like independent living things- 

 These very peculiar and characteristic movements are called 

 ammboid movements. Occasionally a leucocyte may be seen 

 to elongate itself and divide into two (Fig. 26, B) : this is a 

 case of what is called simple fission. The red corpuscles 

 neither move nor divide. 



If a drop of some dye or staining fluid be run in under 

 the cover-glass, the corpuscles will be seen to become rather 

 faint in outline, very transparent, and lightly tinted ; but the 

 most obvious effect is that in the middle of each is seen a 

 rounded or oval granular body {nu) deeply stained by the 

 dye, so as to make a very well-defined coloured area in the 

 interior of the corpuscle. This body is called the nucleus : 

 it is present both in the red and the colourless corpuscles. 



By adding to a fresh drop of blood, in the same manner, 

 a drop of weak acetic acid, the nucleus again becomes 

 distinct, while the body of the corpuscle is rendered very 

 transparent and almost invisible : indeed it finally disappears 

 altogether. It is thus proved that the corpuscles, both red 

 and colourless, consist of two substances, an internal 

 nucleus, stained by dyes, and unaffected by weak acids ; 

 and an external substance, called protoplasm, but slightly 

 affected by dyes, and soluble in weak acids. Both nucleus 

 and protoplasm consist mainly of proteids (p. 72), together 

 with water and a small proportion of mineral matters. 



When distilled water is added to a drop of blood on the 

 slide, the corpuscles are seen to swell up and become partly 

 dissolved, and the red colouring matter of the red corpuscles 

 is dissolved out, the plasma becoming tinged with yellow. 



