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MORPHOLOGICAL APPEARANCE OF CELLS. 533

favorable circuiustaiices they may be seen migrating from the sides of
blood-clots. When at rest the white corpnscles are spheroidal, bnt in
a state of activity they are continually changing in shape. Sometimes
they assume an irregular form, throwing out pseudopodia or prolonga-
tions (Fig. 270, |j), such as are found in the amcieba ; in fact, so strong
is their resemblance to that minute animal that they have been called
the human amoebtTe.
The white blood-cells are lighter than the red, and traverse the
vascular channels upon the periphery of the vessels. They also pass
through the walls of the capillaries, and are found normally in the
various tissues of the body ; in pathological conditions they migrate
in vast numbers. Each pale corpuscle has one or more nuclei, which
are surrounded by a mass of protoplasm unconfined by a cell-wall {g).
By certain methods of staining, the nuclei are demonstrable.
In size the white corpuscles are somewhat larger than the red, aver-
aging about ^^ ^^^ ^^^*^'^ "^ diameter, and they always retain al)out
3 aVo"
the same measurement in different species of animals. They bear to
the red the proportion of 1 to 500.
Besides these red and white cells or corpuscles there may also be seen
in the blood free granules and fine filaments (Fig. 271). Some of the
granules are round (B), others angular. In
some instances the angular granules are con- Fig. 271.
nected with the fine filaments (A), as if they
formed the nucleus from which the filaments
radiate.
The blood-corpuscles and granules can be
washed out from a small quantity of blood
that has been allowed to clot upon a slide,
and there will be nothing left but an opaque,
stringy substance. This white stringy sub-
stance is fibrin, which may now be stained
and examined.
The physiology of the blood is perhaps Fibrin-filaments and Blood-tablets:
A, network of fibrin, shown after
less understood than any other part of the washing away the corpuscles from
animal organism. Many theories have been a preparation of blood that lias
been allowed to clot; many of
advanced as to its origin. It seems most the filaments radiate from small
clumps of blood-tablets. B (from
rational to believe that one which teaches Osier ), blood-corpuscles and ele-
mentary particles or blood-tablets-
that the lymph-corpuscles become altered by within a small vein.
contact with pre-existing white blood-cor-
puscles, and that these in turn are changed into red corpuscles, which in
time disintegrate, their pigment being taken up by their successors.
Prudden, speaking of the origin of blood-cells, says : " Direct observa-
tion has shown that, in some animals at least, the white blood-cells can
multiply by division. Whether the cells which supply the place of
those which seem to be used up in the process of growth and reparation
are produced in this way, and, if so, whether the division occurs in the
blood- or lymph-vessels, or in the cell-spaces of the connective tissue,
or in certain special organs, or whether they are produced in a manner
entirely unknown to us,—these are questions not only of theoretical but
of practical interest; but in spite of much research and the accumula-