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COAGULATION OF THE BLOOD. 319
The thrombokinase does not occur to any appreciable extent in
the circulating blood, but is supplied by the form-elements. The
accelerating action upon coagulation of tissues or parts of tissues depends,
as above stated, upon their content of kinase; but it also in part depends
upon the fact that the tissue fluids excite the secretory activity of the form-
elements.
Fuld l
has arrived at about the same results independently of Mora-
witz, but he has selected other names. The three substances, throm-
bogen, kinase, and thrombin are called by him plasmozym, cytozym,
and holozym. The principal reason why circulating blood remains fluid is,
according to Fuld, because the cytozym is only slowly formed therein
and the ferment (holozym) produced thereby is quickly changed into an
inactive form. Another reason is that the blood contains an antibody
for the fibrin ferment. The assumption of Alexander Schmidt that
the blood contains substances retarding coagulation (anti-thrombins)
has recently also received support by the observations of Fuld and
Spiro, Morawitz, Loeb, Nolf, Pugliese, Howell 2
and others. Accord-
ing to Howell the non-coagulability of circulating blood depends on
the fact that the antithrombin prevents the activation of the prothrombin
into thrombin.
According to the theory of Morawitz, Fuld and Spiro, which is the
most accepted, of those substances necessary for coagulation, only
the thrombokinase (the cytozym) is absent in the circulating blood,
and this is the reason why the circulating blood remains fluid. The
reason why the plasma does not contain any thrombokinase lies in the
fact that the healthy endothelium of the vessels does mot have any irritat-
ing action upon the form-elements, and therefore no mentionable quan-
tity of kinase is given off under these circumstances. Such an elimina-
tion occurs first outside of the blood vessels, and indeed very quickly
in contact with foreign bodies. The formation of thrombin from the
thrombogen takes place in an unknown manner by the action of the
kinase only in the presence of lime salts (in the plasma), and this throm-
bin then transforms the fibrinogen into fibrin.
A serum poor in ferment and having a weak action can be reactivated by the
addition of acid or alkali (Alex. Schmidt, Morawitz), and in this action, accord-
ing to Morawitz, a thrombin (/3) is produced which is somewhat different from
a-thrombin. The ^-thrombin is produced from a special ^-prothrombin which
never occurs in the plasma, but only in the serum. Fuld explains this by
affirming that the a-thrombin is changed in the serum into metazym (/?-pro-
^entralbl. f. Physiol., 17. See also Fuld and Spiro, Hofmeister’s Beitrage, 5.
2
Fuld and Spiro, 1. c; ’Morawitz, 1. c; Loeb, Hofmeister’s Be;
trage, 5; Xolf, Arch,
internat. de Physiol., 6; Pugliese, Biochem. Centralbl., 5, p. 930; Howell, Amer.
Journ. of Physiol., 29.
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