Page 234 - My FlipBook

206 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

[nasmueli as the fermentation of carboliyd rates gives rise to the
production chiefly of lactic acid, and since lactic acid even in
dilute form speedily acts upon tooth-tissue (decalcifies it), there
can be little doubt that the acid reaction and the decalcification
of the dentine are produced in a great part by this acid. The
accuracy of the supposition may be easily proved by the Ewald
test. If we phice a large piece of decayed dentine in a test
tube containing the solution given on page 106, and allow the
tube to stand in the dark for some time, a yellowish zone like a
halo will be formed about the piece, indicating the presence of
lactic acid with tolerable certainty, since we know that the other
substances which give this test (page 107) are not formed except
in very minute quantities.
The acids formed in the mouth by fermentation of starch are
quite as injurious to the teeth as those formed from sugar. The
assertion that starch is not injurious to the teeth rests upon no
experimental basis. On the other hand, it has been irrefutably
established by experiment that saliva containing starch at blood
temperature shows an acid reaction as soon and develops as
much acid in a given space of time as saliva containing sugar.
If we divide a quantity of saliva into a number of equal por-
tions, and add to each an equal quantity of different carbohy-
drates (sugar, bread, potato, starch, etc.), we shall find that those
containing bread and potato not only show an acid reaction
sooner, but even develop more acid in a given time than the
portions to which sugar has been added. Starch-paste and
sugar, as far as my observations go, react about equally strong.
Some very interesting experiments were performed by Ellen-
berger and Hofmeister,^^^ which show that under certain circum-
stances starch-paste, too, is more rapidly transformed into lactic
acid than sugar. An alkalinized pancreas-extract containing
grape-sugar kept at a specified temperature did not develop an
acid reaction till after forty-eight hours or more, whereas on the
addition of starch-paste an acid reaction appeared in twenty-
four liours. " Sugar in statu nascendi seems to be transformed
into lactic acid more quickly than in its ordinary state. In all
experiments on digestion with starch-paste, lactic acid is rapidly
developed."