DESCRIPTION OF PLATES. 159 
Bioop-CorPuscLes. (PuatTES V. AnD VI.) 
The red color of the blood of animals is due 
to the presence of a multitude of colored disks, 
either circular or oval in form, which are sus- 
pended, together with other colorless corpuscular 
elements, in a clear fluid, — the blood-plasma. 
The red blood-corpuscles vary as to shape in 
different classes of vertebrate animals, being cir- 
cular in all the Mammalia except the camel fam- 
ily, and oval in birds, reptiles, and fishes. They 
also vary greatly as to dimensions in different 
genera of the same class. The smallest corpuscles 
known are those of the musk-deer, which only 
measure 73455 Of an inch in diameter; while those 
of the amphiuma, a reptile common in Louisiana 
and other Southern States, measure thirty-five 
times as much, being 34, of an inch in diameter. 
Measurements.of blood-corpuscles always repre- 
sent the average obtained by measuring a con- 
siderable number; for differences exist in the 
diameter of corpuscles contained in the same 
drop of blood. 
In man, the red blood-corpuscles measure about 
zao0 Of an inch in diameter. The blood-corpuscles 
of the dog and of the Guinea-pig approach so 
nearly in size those of man, that it is pretty gen- 
erally agreed among ezpert microscopists that the 
attempt to decide positively, by means. of micro- 
scopical examination and measurements, that cer- 
tain blood-stains submitted for examination in 
