204 BLOOD-DISCS OF MAN AND MAMMALS. 



No nucleus can be distinguished in them, but they present a 

 dark central spot, which is an optical effect of their bi-concave 

 form ; and this spot may be made to disappear by the addition 



T> 



Fig. 115. RED CORPUSCLES OF HUMAN BLOOD. 



Seen separately at A, a a showing the front view, b the profile or edge view, and * a 

 three-quarter view; at B united with each other so as to form columns likepilis 

 of money; at c in a state of alteration such as exposure to air will produca; 

 D shows a colourless corpuscle, or lymph-globule. 



of water to the liquid in which they are suspended, the discs 

 first becoming flat, then bulging-out on either side, and at 

 last swelling so as to burst. The reason of this will be pre- 

 sently explained (231). In MAN and MAMMALS generally, 

 the diameter of these blood-discs varies from about l-2800th to 

 1 -4000th of an inch; but in the small Musk-deer, it is less 

 than 1-1 2,000th. In the Camel tribe, the discs are oval, as 

 in the lower Vertebrata. 



230. In Birds, Reptiles, and Fishes, the blood-particles 

 present some curious differences from those of Mammalia. 

 In the first place, they are much larger ; their form, also, is 

 oval instead of being round ; and instead of being depressed 

 in the centre, they bulge-out on each side. This bulging is 



Fig. 116. BLOOD CORPUSCLES OF PIGEON. 



At A are seen the red corpuscles a, b, and the colourless, or lymph globules c, c; at 

 B, a red corpuscle treated with acetic acid ; and at c, the same treated with water, 

 so as to render the nucleus more distinct. 



evidently occasioned by the presence of a nucleus which is 

 more solid than the rest ; the nucleus, however, is not so well 



