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488 DIGESTION.
the test with tropseolin 00, performed at a moderate temperature as suggested by
Boas, and the test with dimethylamincazobenzene, which is the most delicate,
seem to be the most valuable. If these tests give positive results, then the presence
of hydrochloric acid may be considered as proved. A negative result does not
eliminate the presence of hydrochloric acid, as the delicacy of these reactions
has a limit, and also the simultaneous presence of protein, peptones, and other
bodies influences the reactions more or less. The reactions for lactic acid may
also give negative results in the presence of comparatively large quantities of
hydrochloric acid in the liquid to be tested. Sugar, sulphocyanides, and other
bodies may act with these reagents like lactic acid.
In testing for lactic acid it is safest to shake the material with ether and test
the residue after the evaporation of the solvent. On the evaporation of the ether
the residue may be tested in several ways. Boas utilizes the property possessed
by lactic acid of being converted into aldehyde and formic acid on careful oxida-
tion with sulphuric acid and manganese dioxide. The aldehyde is detected by
its forming iodoform with an alkaline iodine solution or by its forming aldehyde-
mercury with Nessler’s reagent. Croner and Cronheim: x
have suggested
another method.
The quantitative estimation consists in the formation of iodoform with N/10
iodine solution and caustic potash, adding an excess of hydrochloric acid and
titrating with a N/10 sodium-arsenite solution, and retitrating with iodine solu-
tion, after the addition of starch-paste, until a blue coloration is obtained. This
method presupposes the use of ether entirely free from alcohol. For details see
the original publication and the modification of this method suggested by
Jerusalem.2
In order to be able to judge correctly of the value of the different
reagents for free hydrochloric acid, it is naturally of greatest importance
to be clear in regard to what we mean by free hydrochloric acid. It is
a well-known fact that hydrochloric acid combines with proteins, and a
considerable part of the hydrocholoric acid may therefore exist in the
contents of the stomach, after a meal rich in proteins, in combination
with them. This hydrochloric acid combined with proteins cannot
be considered as free, and it is for this reason that certain investigators
consider such methods as those of Sjoqvist, which will be described
below, as of little value. However, it must be remarked that, according
to the unanimous experience of many investigators, the hydrochloric
acid combined with proteins is physiologically active and in this regard
we must refer to the recent investigations of Alb. Muller and J. Schutz.3
Those reactions (color reactions) which only respond to actually free
hydrochloric acid do not show the physiologically active hydrochloric
acid. The suggestion of determining the " physiologically active
"
hydrochloric acid instead of the " free " seems to be correct in principle;
and as the conceptions of free and of physiologically active hydrochloric
acid are not the same, it must always be well defined whether one wishes
to determine the actually free or the physiologically active hydro-
1
Boas. Deutsch. med. Wochenschr., 1803, and Munchener med. Wochenschr. 1893,
Croner and Cronheim, Berl. klin. Wochenschr., 1905. See also Thomas, Zeitschr. f.
physiol. Chem., 50.
2
Bioch. Zeitschr., 12.
8
Alb. Muller, Deutsch. Arch. f. klin. Med., 88, and Pfluger’s Arch., 116; J. Schiitz.
Wien, klin. Wochenschr., 20. and Wien. med. Wochenschr., 1900 (older literature).
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