116 Transaeiions of the Royal Microscopical Society, 
those places where they are pressed upon by the weight of the 
covering glass. The amount of pressure, and also the more or 
less crowded condition of the corpuscles, will determine the degree 
of deviation from the original form. Thus, when a single cor- 
puscle is pressed upon, it will simply enlarge in its horizontal 
diameter, while it is rendered thinner and flat. In the case of a 
group, mutual pressure will come into play, causing the corpuscles 
to assume more elongated or otherwise irregular forms ; or, as it 
frequently happens, when the corpuscles are arranged in a single 
layer, and mutual pressure is exerted upon their margins, they 
will assume a hexagonal form, similar to the cells of a pavement 
epithelium. Finally, when the pressure rests upon a whole mass 
of corpuscles, they may even assume the form of spindles. At the 
same time, the haemoglobin is seen to escape from the blood- 
corpuscles into the surrounding liquor sanguinis. I have observed 
that in cases where the pressure rests upon a mass of corpuscles 
forming the edge of the preparation, their colour appears of a 
dirty brick-red, and darker than in other locahties. The cause of 
this appearance I am unable to determine ; perhaps it is owing to 
some process of oxidation going on at the margin of the drop. 
If now a drop of water is applied to the preparation, and its 
effect upon the mass of distorted blood-corpuscles carefully watched, 
it will be seen that the greater part of them, though fused into 
each other, as they may appear, will gradually separate, and resume 
their original shape. If the pressure be kept up for a long time, 
a portion of the corpuscles, though separating, may not entirely 
resume the round form, but remain more or less distorted. 
When a very small portion of human blood is spread upon a 
glass slide, and, after being covered with the thin plate of glass, a 
drop of water be added to the preparation, it will dilute the liquor 
sanguinis and induce an immediate escape of the haemoglobin 
from the blood-corpuscles, rendering the liquid in the vicinity of 
the latter, according to their number, more or less turbid. At the 
same time the blood-corpuscles will be set in motion, and float 
away into the clearer parts of the liquid. Continuing to part with 
their colouring matter, they are gradually rendered pale, and 
finally appear as mere shadows. If now a portion of the liquid 
is removed by the careful application of a minute point of a piece 
of blotting-paper, and its place filled by a drop of clear water, the 
shadow-like blood-corpuscles will appear bordered by a delicate 
double contour (Fig. 62, a). The central portion of the corpuscle, 
encircled by the inner contour, appears now of the colour of the 
field, while the margin, included by the two contours, appears 
lighter when put in the exact focus. Of course, only a first-class 
objective of sufficient amplification, say one-tenth of an inch, or 
even higher, should be employed for such an examination. 
