100 



COMPARATIVE ZOOLOGY. 



ular, or sac-like, in all animals; but they are constantly 

 changing. The form of the red disks is more permanent, 

 although they are soft and elastic, so that they squeeze 



MAN 



• I 



I. 3200 



ELEPHANT' 



• 



1.274 5 



MOUSE 



• 



1.4268 



MUSK DEER 

 112325 



HUMMING BIRD 



1.2666 

 SNAKE 1 ■ 



PIGEON 

 ^^^^ 



f.2314 



OTEUS ^^MHHI 





Fig. 65.— Comparative Size and Shape of the red Corpuscles of various Animals. 



through very narrow passages. They are oval, circular, 

 or angular, in Fishes ; oval in Reptiles, Birds, and the 

 Camel tribe ; and circular in the rest of Mammals. They 

 are double-convex when nucleated, and double-concave 

 when circular and not nucleated. 



Blood is always heavier than water; but is thinner in 

 cold-blooded than in warm-blooded animals, in herbivores 

 than in carnivores. The blood of Birds, which is the hot- 

 test known, being 10° higher than Man's, is richest in red 

 corpuscles. In Man, they constitute about one half the 

 mass of blood. The white globules are far less numerous 

 than the red; they are relatively more abundant in venous 

 than arterial blood, in the sickly and ill-fed than in the 

 healthy and vigorous, in the lower Vertebrates than in 

 Birds and Mammals. Their number is subject to great 



