58 ANATOMY. 



microscopic elements, such as clustered blood-corpuscles, pigment 

 granules, and caudate cells, the chief of which will be described here- 

 after with the spleen. 



Fig. 38. 



Tig. 38. a (Wagner and Kolliker), three red blood-corpuscles from the frog, one turned on its edge : they 

 show the pale central nucleus and the outer colored part. 6, two red blood-corpuscles of the monk-fish, 

 one seen edgeways, c, two red blood-corpuscles of the common fowl, d, three minute red blood cor- 

 puscles of the goat, e, human capillary vessel from the brain, showing its transparent walls and the 

 nuclei embedded in them ; and also seven red and two white blood-corpuscles within the capillary 

 tube. Magnified 400 diameters, all on the same scale, to show the relative sizes of the different blood 

 corpuscles. 



The red corpuscles, which are present in enormous numbers, and on 

 which the color of the blood entirely depends, are minute circular 

 discs, Fig. 38, e, depressed a little on each side. Seen edgeways they 

 appear rounded at the margins, and they are so soft and flexible as to 

 bend easily around any obstacle (see Fig. 38, e). They are singly of 

 a pale amber color ; but, when collected in numbers, they produce a 

 reddish hue. In blood, drawn from the vessels, the red corpuscles ex- 

 hibit a curious tendency to run together into little rolls like coins : they 

 are heavier than the plasma of the blood. Each corpuscle is usually 

 regarded as a distinct vesicle, or so-called elementary cell, consisting 

 of a very delicate elastic envelope or cell-wall, and a contained soft 

 colored substance : the centre is clearer and paler, and looks like a 

 central body or so-called nucleus, but in the perfect corpuscle there is 

 no distinct nucleus. 



Colored blood-corpuscles in animals. In the mammlferous animals generally, 

 the red corpuscles are also round, disc-like, non-nucleated bodies. In the 

 camel tribe they are elliptical ; in the deer and goat tribes, d, they are circular 

 though small ; they vary in size in different mammalia ; and, so far as is known, 

 are largest in the elephant, and smallest in the musk deer. In birds, c, rep- 

 tiles, amphibia (frogs and newts), a, and most fishes, &, the blood discs are 

 oval, and present a central elevation on each surface. They are larger in birds 

 than in mammalia, still larger in fishes generally, and of yet greater size in the 

 amphibia, being largest of all in the proteus. Their dimensions in a few ani- 

 mals will be given hereafter. In birds, reptiles, amphibia, and fishes, the 

 colored blood-corpuscles are what are termed nucleated cells, possessing, besides 

 an external envelope, a distinct projecting central body or nucleus, and an in- 

 termediate colored substance. In the frog, the nucleus occupies often one-third 

 of the length of the corpuscle ; as it is not visible when the corpuscles are still 

 in the living vessels, it has been supposed by some to be the result of a subse- 

 quent process of aggregation within the corpuscle. 



