or Red Particles of the Mammiferous Animals* 107 
They have a very characteristic appearance, being remarkably 
flat and pellucid, several generally touching at their edges so 
as to form groups, scarcely ever turning over or even moving 
in the fluid. It is obvious from the size, shape, and general 
appearance of these particles, that they are not identical with 
those which have been usually described as the nuclei of the 
blood corpuscles. The average diameter of the disks in the 
first instance was 1 -3429th of an inch. 
Besides the precaution concerning the preservation of the 
blood, it is equally necessary to be careful as to how it is ob- 
tained. The corpuscles are more or less modified very quickly 
after extravasation ; and if some delay occur, and the drop 
of blood, effused into the subcutaneous tissue, require press- 
ure to determine it to the surface, the corpuscles in that 
blood may be expected to be irregular in form and mag- 
nitude, many of them particularly presenting a granulated 
appearance. Hence the glass should not be pressed upon the 
wound, but merely lightly touched on a drop of the blood, 
however small, that has appeared freely immediately after the 
puncture. A specimen thus procured, and dried as before 
noticed, will be excellent, although in all cases where it is 
practicable a small incision directly into a superficial vein will 
be preferable. 
The granulated particles are almost uniformly smaller than 
the common disks, and it is not improbable that some of the 
former may be produced by the irregular shrinking of the 
latter. In some instances I could not detect any of the gra- 
nulated corpuscles in the blood immediately after it was taken 
from the animal, although they were to be seen abundantly 
after a few hours’ exposure in the serum to the atmosphere, 
the temperature ranging between 45° and 50°. In one ob- 
servation some of the extremely minute spherules, which are 
not uncommon in the blood, were observed to attach them- 
selves to a few of the smaller disks, so as to produce the gra- 
nulated appearance. 
The blood corpuscles therefore are so singularly suscep- 
tible of variation in size and form from the operation of very 
slight agency, that there is probably no other microscopic 
object ot equal delicacy, or that requires so much experience 
in its management. Hence it is not surprising that cursory 
observers should have committed remarkable errors, and that 
the history of the blood corpuscles, even after the labours of 
more careful inquirers, should have been so much obscured 
by discrepancies, particularly when it is considered how the 
inherent difiiculties of the subject have been increased by the 
imperfection of instruments. Hewson indeed, whose obser- 
