72 THE BLOOD. 



sidered, if not solid throughout, yet as having no such 

 variety of consistence 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 

 colouring-matter uniformly pervades this, and is not merely 

 surrounded by and mechanically enclosed within the outer 

 wall of the corpuscle. The red corpuscles have no nuclei, 

 although, in their usual state, the unequal 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 a 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 com- 

 monly 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 

 dilution the corpuscles, as already said, may be made to 

 swell up, by absorbing the fluid ; and, if much water be 

 added, they will become spherical and pellucid, their 

 colouring-matter being dissolved, and, as it were, washed 

 out of them. Some of them may thus be burst ; the others 



