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CHAPTER V.
THE BLOOD
The blood is to be considered from a certain standpoint as a fluid
tissue; it consists of a transparent liquid, the blood-plasma, in which
a vast number of solid particles, the red and white blood-corpuscles (and
the blood-plates), are suspended.
Outside of the organism the blood, as is well known, coagulates more
or less quickly; but this coagulation is accomplished generally in a
few minutes after leaving the body. All varieties of blood do not coagulate
with the same degree of rapidity. Some coagulate more quickly, others
more slowly. In vertebrates with nucleated blood-corpuscles (birds,
reptiles, batrachia, and fishes) Delezenne has shown that the blood
coagulates very slowly if it is collected under such precautions that it
does not come in contact with the tissues. On contact with the tissues or
with their extracts it coagulates in a few minutes. The blood with
non-nucleated blood-corpuscles (mammals), on the contrary, coagulates
very rapidly. The coagulation of the blood in these cases may also be
somewhat retarded by preventing the blood from coming in contact
with the tissues (Spangaro, Arthus 1
). Among the varieties of blood
of mammals thus far investigated the blood of the horse coagulates most
slowly. The coagulation may be more or less retarded by quickly cool-
ing; and if we allow equine blood to flow directly from the vein into a
glass cylinder which is not too wide and which has been cooled, and let it
stand at 0° C, the blood may be kept fluid for several days. An upper
amber-yellow layer of plasma gradually separates from a lower red layer
composed of blood-corpuscles with only a little plasma. Between these
is observed a whitish-gray layer which consists of white blood-corpuscles.
The plasma thus obtained and filtered is a clear amber-yellow alkaline
(toward litmus) liquid which remains fluid for some time when kept
at 0° C, but soon coagulates at the ordinary temperature.
The coagulation of the blood may be prevented in other ways. After
the injection of peptone, or, more correctly, proteose solutions into
1
Drlezenne, Corr.pt. rend. soc. de biol., 49; Spangaro, Arch. ital. de Biol., 32;
Arthus, Journ. de Physiol, et Pathol., 4.
250
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