RED BLOOD-CORPUSCLES. 71 



corpuscles may be uniformly diffused through the clot ; 

 but, when it has been slow, the red corpuscles, being the 

 heaviest constituent of the blood, tend by gravitation to 

 accumulate at the bottom of the clot ; and the white cor- 

 puscles, being among the lightest constituents, collect in 

 the upper part, and contribute to the formation of the 

 buffy coat. 



The human red blood-cells or blood corpuscles (figs. 25 and 

 29) are circular flattened disks of different sizes, the majorit}^ 

 varying in diameter from -j--^ to -^oVo" f an inch, and about 

 TTT o'oir f an i nc k i n thickness. When viewed singly, they 

 appear of a pale yellowish tinge ; the deep red colour which 

 they give to the blood being observable in them only when 

 they are seen en masse. Their borders are rounded ; their 

 surfaces, in the perfect and most usual state, slightly con- 

 cave; but they readily acquire flat or convex surfaces 

 when, the liquor sanguinis being diluted, they are swollen 

 by absorption of fluid. They are composed of a colourless, 

 structureless, and transparent filmy framework or stroma 

 infiltrated in all parts by a red colouring-matter termed 

 hamoglobin. The stroma is tough and elastic, so that, as 

 the cells circulate, they admit of elongation and other 

 changes of form, in adaptation to the vessels, yet recover 

 their natural shape as soon as they escape from compres- 

 sion. The term cell, in the sense of a bag or sac, is inap- 

 plicable to the red blood-corpuscle ; and it must be con- 



the case of the oval cells, only the long diameter is here given. It is 

 remarkable, that although the size of the red blood-cells varies so much 

 in the different classes of the vertebrate kingdom, that of the white 

 corpuscles remains comparatively uniform, and thus they are, in some 

 animals, much greater, in others much less than the red corpuscles 

 existing side by side with them. 



It may be here remarked, that the appearance of a nucleus in the red 

 blood-cells of birds, reptiles, amphibia and fish has been shown by Mr. 

 Savory to be the result of post-mortem change ; no nucleus being 

 visible in the cells as they circulate in the living body, or in those 

 which have just escaped from the blood-vessels. 



