Blood-corpuscles of A. tridactylum, &c. By Dr. Schmidt. Ill 
great transparency and refractive power of the protoplasm, of which 
the blood-corpuscle consists, and it is this circumstance which has 
caused those erroneous representations of the profile of this body, 
heretofore alluded to. 
In examining, therefore, a coloured blood-corpuscle in exact 
profile, the contour, which first strikes our eye, is a dark one, 
resembling in shape that of a section of the corpuscle (Fig. 59, &), 
and showing the concavities of the two surfaces. A closer examina- 
tion, however, will reveal two distinct straight lines, being the true 
outlines of the sides of the profile, and extending on each side 
from one convexity of the dark contour to the other, as may be 
seen in examining the drawing. With the least movement made 
by the blood-corpuscle, the view of the exact profile will be lost, 
and a portion of the front surface of the object will be presented. 
At and near the median line the object appears very light, this 
being the part representing the middle of the convex margin, 
where the rays of light, after having passed through the corpuscle, 
undergo the least refraction, and where, moreover, all rays refracted 
at the convex surface, meet in the same focus. Thus, the true 
contour of the profile of the blood-corpuscle in question, in reality 
represented by two straight and parallel lines, connected by two 
semicircular ones, nevertheless includes another contour, repre- 
senting the section of the object. This singular appearance, owing 
to the transparency and the great refracting power of the substance 
of the blood-corpuscle, as well as to its peculiar form, will be 
readily understood by the reader. 
The true profile of the blood-corpuscle is most favourably seen 
when this body is floating in the liquor sanguinis, and turning 
slowly around its long or horizontal axis. Owing to the great 
delicacy of its substance, the corpuscle is very apt to bend upon 
itself in various ways, from the slightest resistance it meets in its 
course when floating in this liquid ; and it is for this reason that 
a good view of the profile is not always obtained. A correct view 
can only be obtained when the corpuscle remains stationary for a 
few seconds, with the full profile turned towards the eye of the 
observer. The slightest motion, as mentioned before, will present 
a portion of one or the other front surface and interrupt the view. 
The colour of a single blood-corpuscle, when seen under the 
microscope, is not a yellow, as has been stated sometimes, but more 
of a light greenish tint. It is only when a number of corpuscles 
are collected into a small mass or group, and resting upon each 
other, that the original greenish tint merges into a yellow. With 
the increase of the thickness of the mass, the yellow becomes 
darker, and finally passes into the scarlet red, as seen in a drop of 
blood. 
Soon after a small drop of human blood has been put on the 
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