106 THE FROG CHAP. 



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 move- 

 ments are called amoeboid 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 (p. 121) be run 

 in under the cover-glass, the corpuscles will be seen to 

 become rather faint in outline, 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 a substance 

 which is known as protoplasm, but slightly affected by 

 dyes, and soluble in weak acids ; and enclosed in this 

 is a nucleus, stained by dyes, and unaffected by weak 

 acids. Both nucleus and protoplasm consist mainly of 

 proteids (p. 72), together with water and a small pro- 

 portion 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 : the red colouring matter of the red 

 corpuscles is dissolved out, the plasma becoming tinged 



