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COMPLAINTS OF THE DIGESTIVE TRACT. 309

its significance, from the fact that the acid produced is speed ily
absorbed, and the contents of the stomach are replaced a numbi r
of times dailv by neutral material. These experiments also show
how small a change in the quantity or quality of the gastric juice
may suflice to render a permanent fermentation ((/ysyje/^^/r/ ch.romc")
in the human stomach possible.
The objection may be urged against these experiments that, in
the solidifit'd condition of the mixture, the HCl could not have
its full etfeet. The control experiments, however, made at the
temperature of the human body (at which the mixture of course
became liquid), confirmed the accuracy of the previous results.
It may be further said that a portion of the HCl disappeared in
combination with bases in the mixture, but I am satisfied, from
experiments not here described, that the loss from this source
must have been very small, and was compensated for by the acid
present in the mixture at the beginning of the experiment, the
reaction in each case being clearly acid.
I next attempted to determine the action of these micro-organ-
isms on carbohydrates, j^articularly their acid-producing power,
being anxious to find the source of the acids of the human
mouth. For this purpose I cultivated them in beef-extract-
sugar solutions, in peptone-sugar solutions, and in milk. Six-
teen of the mouth-bacteria produced an acid reaction, four an
alkaline, and five gave inconstant results. The corresponding-
numbers for the stomach-bacteria were nine, two, and two ; for
the bacteria of the intestines, six, five, and three. The propor-
tion of the acid-forming bacteria in the mouth and stomach is,
according to these results, much greater than in the intestines.
TVIiether this condition is constant or not, could be determined
only by a large number of series of experiments. The cultures
in sterilized milk gave results slightlv different from the above.
It was, furthermore, not possible to draw a sharp line between
those bacteria which produced an acid and those which produced
an alkaline reaction, since in some cases the reaction was only
slight and changed "^-ith time, while in other cases it was
altered by a change in the amount of sugar present. One
bacillus which I tested in reference to this question, cultivated
in 3 per cent, beef-extract solution, left the reaction neutral