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FIBRIN FORMATION. 257
ScHtJTz’s law while on increasing dilution deviates more and more
and finally shows a proportionally slow, and more irregular procedure.
Martin l
has found another law from experiments with plasma and snake-
poisons containing thrombin. According to him the behavior is as
follows: As in the casein coagulation with rennin, the celerity of coagula-
tion is inversely proportional to the quantity of ferment; and Loeb
has observed a similar conduct with invertebrates. The optimum of the
thrombin action lies at about 40° C; at 70-75° C, in neutral solution,
the enzyme is destroyed. According to Howell and Rettger 2
throm-
bin, under proper conditions, can withstand boiling for a short time. The
question as to whether the thrombin found in different animals is the
same substance or whether we have several thrombins, has not been
decided. The latter is not improbable; nevertheless a definite specificity
of different thrombins has not been observed with certainty.
The isolation of thrombin has been tried in several ways. Ordinarily,
it may be prepared by the following method, proposed by Alex. Schmidt:
Precipitate the serum or defibrinated blood with 15-20 vols, of alcohol
and allow it to stand a few- months. The precipitate is then filtered
off and dried over sulphuric acid. The ferment may be extracted from
the dried powder by means of water. Other methods have been suggested
by Hammarsten, Pekelharing, and Howell.3
According to a method
suggested by Hammarsten a solution of thrombin so poor in lime salts
that it contains only 0.3-0.4 p. m. solids and about 0.0007 p. m. CaO
can be prepared.
If a fibrinogen solution containing salt, as above prepared, is treated
with a solution of thrombin, it coagulates at the ordinary temperature
more or less quickly and yields a typical fibrin. Besides the thrombin,
the presence of neutral salts is necessary, for Alex. Schmidt has shown
that fibrin coagulation does not take place without them. The presence
of soluble calcium salts is not, as is generally assumed, a positive con-
dition for the formation of fibrin, because, thrombin can transform
fibrinogen into typical fibrin in the absence of lime salts precipitable by
oxalate.4
The fibrin is not richer in lime than the fibrinogen used in its
preparation if the fibrinogen and thrombin solutions are employed as lime-
free as possible, and the view that the fibrin formation is connected with
a taking up of lime has been shown to be untenable (Hammarsten).
The quantity of fibrin obtained on coagulation is always smaller than
1
Martin, Journ. of Physiol., 32; Fuld, Hofmeister’s Beitrage, 2; Loeb, ibid., 9;
Stromberg, Biochem. Zeitschr., 37.
2
Howell, Amer. Journ. of Physiol., 26; Rettger, ibid., 24.
3
Hammarsten, ibid., 18; Pekelharing, 1. c; Howell, 1. c.
* See Hammarsten, Zeitschr. f. physiol. Chem., 22, which also cites the works of
Schmidt and Pekelharing, and ibid., 28.
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