BLOOD-CORPUSCLES 1 03 5 



double convex, the dark spot disappears ; whilst, on the other hand, 

 it is made more evident when the concavity is increased by the 

 partial shrinkage of the corpuscles, which may be brought about 

 by treating them with fluids of greater density than their own sub- 

 stance. When floating in a sufficiently thick stratum of blood 

 drawn from the body, and placed under a cover-glass, the red 

 corpuscles show a marked tendency to approach one another, adher- 

 ing by their discoidal surfaces so as to present the aspect of a pile 

 of coins ; or, if the stratum be too thin to admit of this, partially 

 overlapping, or simply adhering by their edges, which then become 

 polygonal instead of circular. The size of the red corpuscles is not 

 altogether uniform in the same blood ; thus it varies in that of man 

 from about the ^o^th to the T^Vo^h 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 3oVoth of an inch. The following table l exhibits 



MAMMALS 



Man .... 1-3200 I Camel . . 1-3254, 1-5921 



Dog . . . . 1-3542 | Llama . . 1-3361, 1-6294 



Whale . . . 1-3099 | Javan chevrotain . 1-12325 



Elephant . . . 1-2745 j Caucasian goat . 1-7045 



Mouse . . . 1-3814 \ Two-toed sloth . 1-2865 



BIRDS 



the average dimensions of some of the most interesting examples of 

 the red corpuscles in the four classes of vertebrated animals, expressed 

 in fractions of an inch. Where two measurements are given they 

 are the long and the short diameters of the same corpuscles. (See also 

 fig. 768.) Thus it appears that the smallest red corpuscles known 

 are those of the Javan chevrotain (Tragulus javanicus), whilst the 

 largest are those of that curious group of Batrachia (frog tribe) which 



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

 his edition of Hewson's Works, p. 286 et seq. 



