1036 



VERTEBRATED ANIMALS 



O 



that of man, 

 the former case 



retain the gills through the whole of life ; one of the oval blood-discs 

 of the Proteus, being more than thirty times as long and seventeen 

 times as broad as those of the musk-deer, would cover no 

 fewer than 510 of them. Those of the Amphiuma are still larger. 1 

 According to the estimate of Vierordt, a cubic inch of human 

 blood contains upwards of eighty millions of red corpuscles and 

 nearly a quarter of a million of the colourless. 



The white or ' colourless : corpuscles are more readily distinguished 



in the blood of batrachians 

 than in 

 being in 



of much smaller size, as 

 well as having a circular 

 outline (fig. 766, c) : whilst 

 in the latter their size and 

 contour are so nearly the 

 same that, as the red cor- 

 puscles themselves, when 

 seen in a single layer, have 

 but a very pale hue. the 

 deficiency of colour does 

 not sensibly mark their 

 difference of nature. The 

 proportion of white to red 

 corpuscles being scarcely 

 even greater (in a healthy 

 man) than 1 to 250, and 

 often as low as from one 

 half to one quarter of that 

 ratio, there are seldom 

 many of them to be seen 

 in the field at once ; and 

 these may be recognised 

 rather by their isolation 

 than their colour, espe- 

 FIG. 768. Comparative sizes of red blood cor- cially if the glass cover be 

 puscles: 1, man; a,_ elephant; 3, musk-deer; movec l a little OH the slide, 

 I. droineilar\ ; ... ostrich : t>, pigeon ; 7, humming- 

 bird; 8, crocodile ; ;>, python; 10, proteus ; 11, so as to cause the red cor- 

 perch; 12, pike ; i:-i, shark. puscles to become aggrega 



ted into rows and irregular 



masses. It is remarkable that, notwithstanding the great, variations 

 in the sizes of the red corpuscles in different species of vertebrated ani- 

 mals, the size of the white is extremely constant throughout, their dia- 

 meter being seldom much greater or less than . t -,M M ,th of an inch in the 

 warm-blooded classes and -, -,',,,, th in reptiles. Their ordinary form 

 is globular, but their aspect is subject to considerable variations, 

 which seem to depend in great part upon their phase of development . 



1 A vrr\ ink'i-estiiif,' account "f (lie 'Structure ol I he Red Corpusrlrs of tin- 

 iin 1 1 /iftirfi/l/t>ii ' has ] tc.cn uiven by Dr. II. D. Schmidt, of New Orleans, in 

 the Jonni. Roy. Mir rose. Soc. vol. i. 187H, pp. -''7, !>7. 



