RED BLOOD-CORPUSCLES. 67 



The human red blood-cell* or blood-corpuscles (Figs. 25 and 

 29) are circular flattened disks of different sizes, the majority 

 varying in diameter from 3^00 to 4$^ of an inch, and about 

 TOtWfi f an i ncn i n thickness. When viewed singly, they ap- 



pear of a pale yellowish tinge; the deep red color 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 concave; but they 

 readily acquire flat or convex surfaces when, the liquor san- 

 guinis being diluted, they are swollen by absorption of fluid. 

 They are composed of a colorless, structureless, and transparent 

 filmy framework or stroma, infiltrated in all parts by a red 

 coloring-matter termed hcemoglobin. 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 com- 

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

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

 if not solid throughout, yet as having no such variety of con- 

 sistence in different parts as to justify the notion of its being a 

 membranous sac with fluid contents. The stroma exists in all 

 parts of its substance, and the coloring matter uniformly per- 

 vades this, and is not merely surrounded by and mechanically 

 inclosed within the outer wall of the corpuscle. The red cor- 

 puscles have no nuclei, although in their usual state, the un- 

 equal refraction of transmitted light gives the appearance of a 

 central spot, brighter or darker than the border, according as it 

 is viewed in or out of focus. Their specific gravity is about 1088. 

 In examining a number of red corpuscles with the micro- 

 scope, it is easy to observe certain natural diversities among 

 them, though they may have been all taken from the same 

 part. The great majority, indeed, are very uniform; but some 

 are rather larger, and the larger ones generally appear paler 

 and less exactly circular than the rest ; their surfaces also are 

 usually flat or slightly convex, they often contain a minute 

 shining particle like a nucleolus, and they are lighter than the 

 rest, floating higher in the fluid in which they are placed. 

 Other deviations from the general characters assigned to the 

 corpuscles depend on changes that occur after they are taken 

 from the body. Very commonly they assume a granulated or 

 mulberry-like form, in consequence, apparently, of a peculiar 

 corrugation of their cell-walls. Sometimes, from the same 

 cause, they present a very irregular, jagged, indented, or star- 

 like appearance. The larger cells are much less liable to this 

 change than the smaller, and the natural shape may be restored 

 by diluting the fluid in which the corpuscles float ; by such 



