rpuscles are regular in shape, and float about, and tumble
freely over one another, the colorless are of irregular shape, and stick
close to the glass slide on which they are placed. Again, while the red
corpuscles are changed only by some influence from without, as pressure
and the like, the colorless corpuscles spontaneously undergo active and
very curious changes of form, resembling those of the amoeba, a very
minute organism found in stagnant water (Fig. 2).

The number of both red and colorless corpuscles varies a great deal from
time to time. For instance, the number of the latter increases after
meals, and quickly diminishes. There is reason to think both kinds of
corpuscles are continually being destroyed, their place being supplied by
new ones. While the action of the colorless corpuscles is important to the
lymph and the chyle, and in the coagulation of the blood, their real
function has not been ascertained.

[Illustration: Fig. 66.--Blood Corpuscles of Man.

A, red corpuscles;
B, the same seen edgeways;
C, the same arranged in rows;
D, white corpuscles with nuclei.
]

Experiment 85. _To show the blood corpuscles_. A moderately
powerful microscope is necessary to examine blood corpuscles. Let a
small drop of blood (easily obtained by pricking the finger with a
needle) be placed upon a clean slip of glass, and covered with thin
glass, such as is ordinarily used for microscopic purposes.

The blood is thus spread out into a film and may be readily examined. At
first the red corpuscles will be seen as pale, disk-like bodies floating
in the clear fluid. Soon they will be observed to stick to each other by
their flattened faces, so as to form rows. The colorless corpuscles are
to be seen among the red ones, but are much less numerous.

182. The Coagulation of the Blood. Blood when shed from the living
body is as fluid as water. But it soon becomes viscid, and flows less
readily from one vessel to another. Soon the whole mass becomes a nearly
solid jelly called a clot. The vessel containing it even can be
turned upside down, without a drop of blood being spilled. If carefully
shaken out, the mass will form a complete mould of the vessel.

At first the clot includes the whole mass of blood, takes the shape of
the vessel in which it is contained, and is of a uniform color. But in a
short time a pale yellowish fluid begins to ooze out, and to collect on
the surface. The clot gradua