302 



COMPARATIVE ZOOLOGY 



lating, and containing white corpuscles. The blood of 

 the vertebrates, apparently a clear, homogeneous liquid, 

 really consists of minute grains, or globules, of organic 

 mattep floating in a fluid. If the blood of a frog be 

 poured on a filter of blotting paper, a transparent fluid 

 (called plasma} will pass through, leaving red particles, 

 resembling sand, on the upper surface. Under the mi- 

 croscope, these particles prove to be cells, or flattened 

 disks (called corpuscles^ containing a nucleus ; some are 

 colorless, and others red. In mammals the red disks 



E 



FIG. 259. Blood Corpuscles: A, red corpuscles in rouleaux, a, a, colorless corpuscles, 

 magnified about 400 times; B, red corpuscles in focus; C, view of edge; D, three- 

 quarters view; E, red corpuscle swollen with water; F, G, H, distorted red corpuscles. 



have a tendency to collect together into piles ; the color- 

 less ones remain single. Meanwhile, the plasma sepa- 

 rates into two parts by coagulating ; that is, minute 

 fibers form, consisting si fibrin, leaving a pale yellowish 

 fluid, called serum. m Had the blood not been filtered, 

 the corpuscles and fibrin would have mingled, forming 

 a jelly like mass, known as clot. Further, the serum will 

 coagulate if heated, dividing into hardened albumen and 

 a watery fluid, called serosity, which contains the soluble 

 salts of the blood. 



These several parts may be expressed thus : 



Blood 



Corpuscles 



Plasma 



colored 



fibrin 

 serum 



( albumen. 



\ serosity = water and salts. 



