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 
A a & B Cc 
D 
Fig. 115.—RrEp CorruscLes or HumMAw Bioop. 
Seen separately at a, aa 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 like piles 
of money; atcin a state of alteration such as exposure to air will produce; 
D shows a colourless vorpuscle, 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 Mammats generally, 
the diameter of these blood-dises varies from about 1-2800th to 
1-4000th of an inch; but in the small Musk-deer, it is less 
than 1-12,000th. 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 
> 
a aed 
Fig. 116.—Btoop CorpuscLes oF PiGEoN. 
At a are seen the red corpuscles a, 5, and the colourless, or lymph globules e¢, ¢; at 
B, ared corpuscle treated with acetic acid; and at c, the same treated with water, 
80 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 
