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PEPSIN DIGESTION. 471
tory. 1
Sulphuric acid, it seems, has a weaker action than the other
inorganic acids. The degree of acidity is also of the greatest importance.
With hydrochloric acid the degree of acidity is not the same for differ-
ent protein bodies. For fibrin it is 0.8-1 p. m., for myosin, casein, and
vegetable proteins about 1 p. m., for coagulated egg albumin, on the
contrary, about 2.5 p. m. In regard to the dependence of the extent
of transformation upon the quantity of enzyme and the time of diges-
tion we refer to page 58. The kind of protein is of importance, for
example, for besides what was said above in regard to the fibrin, hard-
boiled egg albumin is much easier digested by an acidity of 1-2 p. m.
HC1 than liquid egg albumin, which is rather resistant to the action
of gastric juice. The accumulation of products of digestion has a retard-
ing action on digestion (page 65), although, according to Chittenden
and Amerman,2
the removal of the digestion products by means of dialysis
does not essentially change the relation between the proteoses and true
peptones. Pepsin acts more slowly at low temperatures than it does at
higher ones. It is even active in the neighborhood of 0° C, but with
increasing temperature the rapidity of digestion also increases until
about 40° C, when the maximum is reached. If the swelling up of the
protein is prevented, as by the addition of neutral salts, such as NaCl,
in sufficient amounts, or by the addition of bile to the acid liquid,
digestion can be prevented to a greater or less extent. Foreign bodies
of different kinds produce dissimilar effects, in which naturally the
variable quantities in which they are added are of the greatest impor-
tance. Salicylic acid and carbolic acid, and especially sulphates
(Pfleiderer), retard digestion, while arsenious acid promotes it (Chit-
tenden), and hydrocyanic acid is relatively indifferent. Salts of the
alkali and alkaline earth metals have a strong retarding action in strong
concentration. By experiments with salt solutions so strongly diluted
that the action, on account of the strong dissociation, was brought about
by ions and not by the electrolytically neutral molecules (min. -fa and
max. I normal salt solutions), J. Schutz 3
found that the anions had a
much greater retarding action upon pepsin digestion than the cations.
Of these latter the sodium cation had the strongest retarding action.
Alcohol in large quantities (10 per cent and above) disturbs the digestion,
while small quantities act indifferently. Metallic salts in very small
quantities may indeed sometimes accelerate digestion, but otherwise
1
See Wr6blewski, Zeitschr. f. physiol. Chem., 21, and especially Pfleiderer, Pfliiger’s
Arch., 66, which also gives references to other works; Larin, Biochem. Centralbl., 1,
484; and A. Pick, Wein. Sitzungsber., M. N. Klasse, 112.
* Journ. of Physiol. 14.
1
Hofmeister’s Beitriige, 5.
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