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40 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

a violet color. Alcohol, acetic acid, etc., cause a white flaky or
fibrous precipitate.
Lastly, humau saliva invariably contains a diastatic ferment,
called ptyaline, which is identical with that found in the secre-
tion of the pancreatic glands, in the juices of the stomach and
intestines, in blood-corpuscles, in the liver, in the secretion of the
tonsils, etc. This ferment also occurs in the saliva of guinea-
pigs and rabbits, rarely in that of dogs (Hoppe-Seyler) ; Roux ^^
failed to detect it in the saliva of horses. Ellenberger and Hof-
meister, on the other hand, invariably found ptyaline in the
saliva of dogs and horses.
Through the action of ptyaline, starch is converted into dex-
trine and a kind of sugar (called ptj-alose by Nasse), which is
directly fermentable and has the property of reducing the oxide
of copper. The process of saccharification begins instantly, so
that it is immaterial for the ensuing fermentation whether the
saliva be mixed with starch or with sugar. Theoretically, the
acid reaction would set in at the same time and with equal in-
tensity in both cases. Indeed, it seems as if saliva mixed with
starch ferments not only sooner, but also forms a larger quantity
of acid than sugar. (See Chapter YIII.)
Ptyaline is able to convert comparatively large, though not
unlimited, quantities of amylum into sugar. In an experiment
made by Kriiger, 4.672 grams of amylum were converted into
ptyalose by 1 gram of pancreatic juice, within the space of thirty
minutes. Xow, since 1 gram of pancreatic juice contains only
0.014 of organic matter, of which, again, the ferment represents
but a small fraction, it is evident that 1 gram of the ferment can
transform a multiple of 314 grams of amylum into sugar in half
an hour. Ptyaline difl:ers from the vegetable diastase, (1) in the
dissimilarity in the sugars formed ; in the latter case, not ptya-
lose, but maltose, is produced ; (2) in respect to the very ditfer-
ent temperatures at which the ferments are most active, ptyaline
acting most rapidly at 35° to 40^ C, vegetable diastase at 70° C.
A'suflicient quantity of pure saliva for the purpose of experi-
mentation may be obtained, after very thoroughly cleansing the
teeth and entire. oral cavity, by placing a crystal of muriate of
cocaine upon the back of the tongue or by painting the surface