RED CORPUSCLES or BLOOD. 599 



"red," and the "white" or "colorless." The former present, in 

 every instance, the form of a flattened disk, which is circular in 

 Man and in most Mammalia (Fig. 315), but which is oval in 

 Birds, Reptiles (Fig. 314), and Fishes, and in a few Mammals 

 (all belonging to the Camel tribe) ; in the one form as in the 

 other, this disk is a flattened cell, whose walls are pellucid and 

 colorless, but whose contents are colored. They may be caused 

 to swell up and burst, however, by the imbibition of water ; and 

 the perfect transparency and the homogeneous character of their 

 walls then become evident. The "red corpuscles" in the blood 

 of Oviparous Yertebrata are distinguished by the presence of a 

 distinct central spot or nucleus, which appears to be composed of 

 an aggregation of minute granules ; this is most distinctly brought 

 into view by treating the blood-disks with acetic acid, which 

 renders the remaining portion extremely transparent, while it 

 increases the opacity of the nucleus (Fig. 314, d). It is remark- 

 able, however, that the "red corpuscles" of the blood of Mam- 

 mals should possess no obvious nucleus ; the dark spot which is 

 seen in their centre (Fig. 315, 6), being merely an effect of refrac- 



FIG. 3J4. 



Fig. 314. Red Corpuscles of Frog's Blood:!, 1, their flattened face; 2, particle turned nearly 

 edgeways; 3, colorless corpuscle ; 4, red corpuscles altered by dilute acetic acid. 



Fig. 315. Red Corpuscles of Human Blood: represented at , as they are seen when rather 

 within the focus of the microscope, and at 6, as they appear when precisely in the focus. 



tion, consequent upon the double concave form of the disk. When 

 the corpuscles are treated with water, so that their form becomes 

 first flat, and then double convex, ihe dark spot disappears; 

 whilst, -on the other hand, it is made more evident when the 

 concavity is increased by the partial emptying of the cell, which 

 may be accomplished by treating the blood-corpuscles with fluids 

 of greater density than their own contents. The size of the " red 

 corpuscles" is not altogether uniform in the same blood; thus it 

 varies in that of Man, from about l-4000th to the l-2800th of an 

 inch. But we generally find that there is an average size, which 

 is pretty constantly maintained among the different individuals 

 of the same species ; that of Man may be stated at about l-3200th 

 of an inch. The following Table 1 exhibits the average dimen- 



1 These measurements are chiefly selected from those given by Mr. Gulliver in his 

 edition of Hewson's Works, p. 236, et seq. 



