ITS PHYSICAL, CHEMICAL, AND STRUCTURAL CHARACTERS. 159 



140. In all Oviparous Vertebrata, without any known exception, the Red 

 Corpuscles are oval the proportion be- 

 tween their long and their short diame- Fi S- 12 - 



ters, however, being much subject to 

 variation } and their nuclei may always 

 be brought into view, by treatment with 

 acetic acid, when not at first visible. 

 In the red particles of the Frog, which 

 are far larger than those of Man, a nu- 

 cleus can be observed to project some- 

 what from the central portion of the 

 oval, even during their circulation (Fig. 

 12, 1, 1) ; and it is brought into extreme Red Corpugcleg of Frog , s Blood . 1; 1? their flat _ 



distinctness by the action Of acetic acid, tened face; 2 , particle turned nearly edgewise; 3, 

 Which renders the remainder of the par- lymph-globule; 4, red corpuscles altered by dilute 

 tide extremely transparent, whilst it acetic acid. Magnified 500 diameters. 



gives increased opacity to the nucleus, 



which is then seen to consist of a granular substance (4). In the still larger 

 blood-disk of the Proteus and Siren, this appearance is yet more distinct ; the 

 structure of the nucleus being so evident, without the addition of acetic acid, 

 that its granules can be counted. 1 



141. The form of the Red Corpuscles is not unfrequently seen to change 

 during their circulation ; but this is generally in consequence of pressure, from 

 the effects of which, however, they quickly recover themselves. In the capil- 

 lary vessels, they sometimes become suddenly elongated, twisted, or bent, 

 through a narrowing of the channel ; and this change may take place to such a 

 degree as to enable the disk to pass through an aperture, which appears very 

 minute in proportion to its diameter. When undergoing spontaneous decompo- 

 sition, the blood-disks become granulated, and sometimes (as long since noticed 

 by Hewson) even mulberry-shaped ; and particles in which these changes appear 

 to be commencing, may be found in the blood at all times. The size of the 

 blood-disks is liable to considerable variation, even in the same individual ; some 

 being met with as much as one-third larger, whilst others are one-third smaller, 

 than the average. The diameter of the corpuscles bears no constant relation to 

 the size of the animal, even within the limits of the same class ; thus, although 

 those of the Elephant are the largest among Mammalia (as far as is hitherto 

 known), those of the Mouse tribe are far from being the smallest; being, in fact, 

 more than three times the diameter of those of the Musk Beer. There is, how- 

 ever, as Mr. Gulliver has remarked, a more uniform relation between the size 

 of the animal and that of its blood-disks, when the comparison is made within 

 the limits of the same order. In Man, their diameter varies from about l-4000th 

 to l-2800th of an inch, the average diameter being probably about l-8200th ; 

 and their average thickness, according to the same excellent observer, is about 

 l-12,400th of an inch. 2 The color of the Red Corpuscles is very pale when they 

 are lying in a single stratum ; and it is only when we see three or four super- 

 posed one upon another, that the full deep-red tint of their contents becomes 

 apparent. The cause of the difference in hue between the corpuscles of arterial 

 and those of venous blood will be considered hereafter ( 166). 



1 See " Penny Cyclopaedia," Art. "Siren." 



2 A Tabular summary of Mr. Gulliver's very numerous and accurate measurements of 

 the Red Corpuscles of the Blood of different animals, from all the classes and most of the 

 orders of the Vertebrate series, is contained in the "Proceedings of the Zoological Society," 

 No. cii., and also in his Edition of the "Works of Hewson," already referred to, published 

 by the Sydenham Society (p. 237). From these, the following measurements of the blood 

 of domestic animals (expressed in fractions of an English inch) maybe selected, as the most 



