342 PHILOSOPHY OF ZOOLOGY. 



die 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. 

 YOUNG 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 f." AMICI 

 has found them of two kinds, both with angular margins ; 

 but, in the one, the centre is depressed on both sides ; while, 

 in the other, it is elevated j. 



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, suiTounded 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 KATER, WOL- 

 LASTOX, YOUNG, and BAUER, give the diameter of each par- 

 ticle a range from T y 1 ^ ^th part of an inch, to 5 ^ s 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 is no proportion 



Phil. Trans, vol. Ixiii. p. 310. 

 f Annals of Philosophy, vol. ii. p. 116. 

 + Edin. Med. and Surg. Journ, vol. xv. p. 120. 



II Mr HEWSON has given figures of the particles of the Wood in a variety 

 of different animals, in Phil. Trans. Ixiii. tab. xii. 



