CHAP. VII BLOOD CORPUSCLES 105 



that the light passes through two or three layers of them to 

 reach the eye, they will appear red : they are- hence called red 

 corpuscles. Frequently they are seen turned on edge (D), 

 and their appearance in this position shows them to be flat 

 oval discs with a swelling in the centre. They are about 

 j^th of a millimetre (about txVtj'^^^ inch) in long diameter. 

 Among the red corpuscles are found, in much smaller 

 numbers, bodies (Fig. 26, A) not more than half the long dia- 

 meter of the red corpuscles in size, quite colourless, distinctly 

 granular — so as to have the appearance of ground glass — 



D 



FlCi. 26. — Blood corpuscles of the frog, highly magnified. 

 A, colourless corpuscle ; B, the same in process of division ; C, red corpuscle, 

 surface view ; D, the same, edge view, nu, nucleus. (From Parker's Biology. 



and with a slightly irregular outline. These are the colour- 

 less corpuscles or leucocytes. They are not flat, like the red 

 corpuscles, but have the form of irregular lumps. 



The plasma, like the leucocytes, is quite colourless, so that 

 the colour of the blood is seen to be due entirely to the 

 large number of red corpuscles it contains. 



If the drop of blood has been prepared and examined 

 under the high power with sufficient rapidity, a remarkable 

 phenomenon can be made out with regard to the colourless 

 corpuscles. This can be most easily demonstrated by making 

 a series of outline sketches of the same leucocyte at intervals 

 of a minute or two. You will then notice that the sketches 

 all differ from one another : in one there will perhaps be a 

 little projection going off to the right ; in the next this will 

 have disappeared and a similar projection will have appeared 



