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474 DIGESTION.
Rennin or (thymosin is the enzyme, which is especially character-
ized by the fact that it coagulates milk or casein solutions containing
lime in neutral or indeed faintly alkaline reaction. It must probably
be considered as a proteolytic enzyme. Rennin is habitually found in
the neutral, watery infusion of the fourth stomach of the calf and sheep,
especially in an infusion of the fundus part. In other mammals and in
birds it is seldom found, and in fishes hardly ever in the neutral infusion.
In these cases, as in man and the higher animals, a rennin-forming sub-
tance, a rennin zymogen, occurs, which is converted into rennin by the
action of an acid (Hammarsten) . Hedin has obtained a retarding
solution by treating a neutral infusion of the stomachs of various animals
with dilute ammonia and then neutralizing. These solutions entirely
or partly retard the action of the rennin from the same animal and is
destroyed by acid with the setting free of rennin. Hedin therefore
considers the rennin zymogen as a combination between rennin and an
inhibitory substance, in which combination the inhibitory body is
destroyed by treatment with acid; consequently the rennin appears in
an active form.
According to Bang the rennin of the human and pig stomachs differs
from that of the calf’s stomach in being much more resistant to acids,
more easily destroyed by alkalies, and that its action is much more
accelerated by calcium chloride than that from the calf’s stomach.1
Active rennin occurs in the human stomach under physiological condi-
tions, but may be absent under special pathological conditions.2
According to the experience of Hammarsten the rennin of the pike
and of the dog differs from that of the calf, and Hedin 3
finds in the specific
kind of inhibitory action of rennin produced by means of ammonia
treatment as well as by immune serum, a proof that the rennin enzyme
of different kinds of animals differ more or less from each other. In
regard to this inhibition see pages 62-64.
Enzymes having a rennin action has also been found in the blood
and several organs of higher animals as well as in invertebrates. Sim-
ilar enzymes are also very widely distributed in the plant kingdom and
numerous micro-organisms have the ability to produce rennin.
1
Deutsch. med. Wochenschr., 1899, and Pfliiger’s Arch., 79.
2
Schumburg, Virchow’s Arch., 97. A good review of the literature may be found
in Szydlowski, Beitrage zur Kenntnis des Labenzym nach Beobaehtungen an Saug-
lingen, Jahrb. f. Kinderheilkunde (N. !\), 34. See also Lorcher, Pfliiger’s Arch., 69.
which also contains the pertinent literature. An excellent review of the literature
on rennin and its action may be found in E. Fuld, Ergebnisse der Physiol., 1, Abt. 1,
468.
3
Hammarsten, Upsala Liikaref. forh. 8, 78 (1872). Zeitschr. f. physiol. Chem.
56, 18 (1908), 68, 119 (1910); Hedin, ibid. 72, 187, 74, 242, 76, 355 (1911), 77, 229 (1912).
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