1036 



VERTEBEATED ANIMALS 



.00 O f '0 



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 that of man, 

 being in the former case 

 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; 2, elephant; 3, musk-deer; TO/] Q li-H-lo , n the. lirlA 

 4, dromedary ; 5, ostrich ; 6, pigeon ; 7, humming- m Ved a Mt > 



bird ; 8, crocodile ; 9, python ; 10, proteus ; 11, SO as to cause the red cor- 

 perch ; 12, pike ; 13, 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 -^nnrth of an inch in the 

 warm-blooded classes and ^Voth 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. 



10 



1 A very interesting account of the ' Structure of the Red Corpuscles of the 

 Amphiuma tridactylum ' has been given by Dr. H. D. Schmidt, of New Orleans, in 

 the Journ. Hoy. Microsc. Soc. vol. i. 1879, pp. 57, 97. 



