786 
THE FORM AND COMPARATIVE SIZE OF THE 
BLOOD-DISCS IN VARIOUS ANIMALS. 
By Richard Owen, Esq., F.R.S., F.L.S., F.G.S., and Hunterian 
Professor in the Royal College of Surgeons. 
If the determination of the size and form of the red particles of 
the blood in different species of animals be a matter of interest to 
the general physiologist, it must still more nearly concern the ve- 
terinary surgeon, under whose immediate care and observation the 
diseases of so many of the mammiferous animals properly fall. 
It may be superfluous to remark to your intelligent readers, that 
the red particles, improperly called “ blood globules,” are minute 
flattened plates, or discs, in all the four classes of vertebrated ani- 
mals ; that these discs have a circular form in all the mammalia 
in which they have been hitherto observed, with the exception of 
the dromedary and llama, where they are elliptical ; that they 
have an elliptical form in birds and reptiles, and in the majority 
of fishes. The size of the blood-discs bears no proportion to the 
bulk of the animal : they are largest in the cold-blooded amphibia ; 
and in this class their size appears to relate to the length of time 
during which the external gills are preserved. Thus the newt has 
larger blood-discs than the frog or toad, and preserves its external 
gills during a longer time ; and the proteus, which never loses the 
external gills, has still larger blood-discs. In this animal, indeed, 
they are visible to the naked eye ; but in other other species a mi- 
croscope, and generally of a high power, is required to distinguish 
their form. The size of the blood-discs has been determined in 
the following animals to be in fractions of an inch : — 
Proteus (long diameter) 
Newt (ditto) 
Frog (ditto) 
Tortoise (ditto) 
Common Fowl (ditto) . 
Ox 
Man 
T5T 
whs 
Wish 
T2 r*j 
TSST 
TiW 
TsW 
Having already received your valuable assistance in obtaining 
blood from your patients in the Zoological Gardens for pursuing 
this comparison, I beg to submit to you the results obtained from 
the following species : — 
ORDER, 
Pachydermata Elephant ( Elephas Indicus ), male, nearly full grown. 
Rhinoceros ( Rhinoceros Indicus ), male, full grown. 
Ruminantia Dromedary ( Camelus Dromedarius ), male, full grown. 
Giraffe ( Camelopardalis Girciffa ), male, nearly full grown. 
Edentata Armadillo ( Dasypus 6-cinctus ), male, full grown. 
