OF THE BLOOD. 



47 



however, they are elliptic. In birds, reptiles, batrachia, and 

 fishes, they are elliptic (Fig. 37.) 



The corpuscles are always microscopic; and in (g) 

 man, and in mammals generally, they are extremely (^ *=* 

 small. In man, the dog, rabbit, and some others, \3J ^ 

 their diameter is from the three-thousandth to the -p. 36 * 

 four-thousandth part of an inch. 



In birds, the globules are larger than in mammals. In 

 the reptiles and batrachia they are still larger. In the proteus 

 they attain their maximum. 



Finally, in fishes, the blood globules ^ 



are intermediate between those of birds 

 and the batrachia. 



Moreover, the blood globules are 

 always flattened, and present a central 

 spot or nucleus, surrounded with a rim 

 or border. Their structure is extremely 

 difficult to be clearly made out ; but 

 when seen to most advantage, they seem 

 to be composed of a central nucleus and 

 an envelope resembling a bladder. This 

 envelope being depressed, gives to the 

 globule the appearance of a disc swollen 

 in the middle. It is of a reddish colour, 

 and seems formed of a substance re- 

 sembling jelly, but very elastic. The central nucleus is of a 

 spheroidal form, and is not coloured. In mammals the 

 nucleus is not distinct, and the central portion is depressed ; 

 but analogy induces us to suppose that, as in other animals, 

 it is also present in man. 



Other globules, spherical and colourless, exist in the blood, 

 resembling greatly those observed in the chyle ; from being 

 mingled with the red globules they are not readily ob- 

 served. 



82. In the white blood of the invertebrate kingdom, 

 globules are also found, but different from those described ; 

 the size varies much in the same individual, and their surface 

 has a raspberry appearance; their form is generally spherical, 



* Globules of the human blood, magnified nearly 400 times (in diameter). 



f Elliptic globules of the blood in birds, batrachia, and fishes ; a, 

 globules of the blood in the domestic fowl, seen in profile; b, globules 

 of the blood in the frog; c, globules of the blood in a fish of the shark kind 

 (equally magnified) . 



Fig. 37.f 



