354 



PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



comes the all-purifier. (3) It takes oxygen to every 

 tissue to consume waste and food by combustion, and 

 thus generates heat and force, and thus becomes the 

 all-warmer and energizer. (4) It acts also as a reservoir, 

 especially for food. The food taken to-day is not used 

 to-day, but the blood is drawn upon for heat and force 

 and tissue repair and again resupplied. The blood is 

 like a lake in irrigation or a bank in currency. (5) To 

 a much less extent it is also a reservoir for waste ; to a 

 less extent because the urgency of waste removal is 

 much greater. 



Comparative Morphology of Blood. — In all ver- 

 tebrates we have two kinds of globules, the red and the 

 white. The white, or leucocytes, are substantially simi- 

 lar in all ; but the red differ in size, shape, and structure 

 in the different classes. 



1. Mammalian Blood. — The blood of all mammals 

 (Fig. 237) is substantially similar to that of man, already 

 described. The red corpuscles (globules) are all small 

 circular, non-nucleated disks. The only exception in shape 

 is in the camel, in which they are elliptic instead of cir- 

 cular, but otherwise they are as stated above. In size 

 they bear no apparent relation to the size of the animal ; 

 those of a mouse, on the one hand, and of an elephant, 

 on the other, not differing in any marked degree from 

 that of man. Even expert microscopists are in doubt 

 whether the blood of a dog can be certainly distin- 

 guished from that of a man. 



All mammals (except monotremes) are viviparous or 

 young-bearing. Therefore this style of blood may be 

 called viviparous vertebrate blood. 



2. Birds, Reptiles, Amphibians, and Fishes. — All other 

 classes of vertebrates — viz., birds, reptiles, amphibians, 

 and fishes — have blood globules differing in size, shape, 

 and structure from those of mammals, but similar to one 



