342 PHILOSOPHY OF ZOOLOGY. 
dle only it fills, and whose edges are hollow, and either 
empty, or filled with a subtile fluid *.” The form of the 
particles in some animals, he found to be oval, as LEEUEN- 
HOEK had previously observed, and in others circular. 
Youne admits, that * their axis is sometimes not more 
than one-third or one-fourth of their greatest diameter,” 
and that they resemble a soft substance with a denser nu- 
cleus, not altogether unlike the crystalline lens, together 
with the vitreous humour, as seen from behind +.” Amicr 
has found them of two kinds, both with angular margins ; 
but, in the one, the centre is depressed on both sides ; while, 
m the other, it is elevated ¢. 
Independent of these discrepancies in the results of dif- 
ferent observers, it appears to be the general opinion at pre- 
sent, that the particles of the blood consist of a dense nu- 
cleus, surrounded by a film of matter of less consistence ; 
and that the particles of the blood of some animals, as man, 
are circular ; while, in others, as the skate, they are oval |. 
The size of these particles of the blood has not been sa- 
tisfactorily determined, as considerable difference prevails 
in the result of their measurement, even when the blood of 
the same animal has been subjected to the micrometer by 
different observers. ‘The measurements of Katrr, Wot- 
LASTON, Younc, and BavEn, give the diameter of each par- 
ticle a range from , =, 5th part of an inch, to ,,),,;th. From 
the testimony of several observers, it appears, that, in the 
same blood, the particles are not all of equal size, and that 
the particles of the blood of different animals exhibit diffe- 
rent magnitudes. In this last case, there 1s no proportion 
* Phil. Trans, vol. lxiii. p. 310. 
+ Annals of Philosophy, vol. ii. p. 116. 
+ Edin. Med. and Surg. Journ, vol. xv. p. 120. 
!| Mr Hewsow has given figures of the particles of the blood in a variety 
of different animals, in Phil. Trans. Ixiii. tab. xii. 
