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472 DIGESTION.
they tend to retard it. The action of metallic salts in different cases
can be explained in various ways, but they often seem to form with pro-
teins insoluble or difficultly soluble combinations. The alkaloids may
also retard the pepsin digestion (Chittenden and Allen 1
). A very
large number of observations have been made in regard to the action
of foreign substances on artificial pepsin digestion, but as these observa-
tions have not given any direct result in regard to the action of the
same substances in natural digestion, as well as upon secretion and
absorption, we will not discuss them here.
The Products of the Digestion of Proteins by Means of Pepsin and Acid.
In the digestion of nucleoproteins or nucleoalbumins an insoluble residue
of nuclein or pseudonuclein always remains, although under certain
circumstances a complete solution may occur. Fibrin also yields an
insoluble residue, which consists, at least in great part, of nuclein,
derived from the form-elements inclosed in the blood-clot. This residue
which remains after the digestion of certain proteins was called dyspep-
tone by Meissner. This name is therefore not only unnecessary but
indeed erroneous, as this residue does not consist of bodies related to the
peptones. In the digestion of proteins, substances similar to acid albu-
minates, parapeptone (Meissner 2
), antialbumate, and antialbumid
(Kuhne), may also be formed. On separating these bodies the filtered
liquid, neutralized at boiling-point, contains proteoses and peptones in
the old sense, while the so-called Kuhne true peptone and the other
cleavage products are obtained only after a longer and more intense
digestion. The relation, between the proteoses, changes very much in
different cases and in the digestion of the proteins. For instance, a larger
quantity of primary proteoses is obtained from fibrin than from hard-
boiled egg albumin or from the proteins of meat; and the different
proteins, according to the researches of Klug,3
yield on pepsin diges-
tion unequal quantities of the various digestive products. In the diges-
tion of unboiled fibrin an intermediate product may be obtained in the
earlier stages of the digestion—a globulin which coagulates at 55° C
(Hasebroek 4
). For information in regard to the different proteoses
and peptones which are formed in pepsin digestion see pages 127 to 136.
Action of Pepsin-Hydrochloric Acid on Other Bodies. The gelatin-
forming substances of the connective tissue, of the cartilage, and of the
1
.Studies from the Lab. Physiol. Chem. Yale University, 1, 76. See also Chitten-
den and Stewart, ibid. 3, 60.
2
Tlie works of Meissner on pepsin digestion are found in Zeitschr. f. rat. Med., 7,
8, 10, 12, and 14.
» Pfluger’s Arch., 65.
4
Zeitschr. f. physiol. Chem., 11.
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