Page 200 - My FlipBook

NINETEENTH LECTURE.

In a previous lecture I had something to say of acidity of
the saHva and the cause of this acidity. You will remem-
ber that I gave the cause as the growth of micro-organ-
isms in the saliva. I should have had illustrations of this
before you earlier, but I have had considerable trouble in
getting suitable culture media. I have some now by which
I can illustrate the development of acidity, that I will pass
among you. I have put in each tray two tubes of clear
broth and two tubes with litmus added. You can hold be-
tween you and the light and see that they are blue. The
media is a beef broth to which a little ordinary sugar has
been added. (Passes tubes to class.)
I have in this other tray a number of tubes of the litmus
broth in which I will make some plants from saliva, and I
would like to steal a little time from someone else to-mor-
row morning to show them to you. By next Monday they
will all be grown and fallen down and you will not get
quite the idea of the promptness with which this color is
changed as you will get by seeing them to-morrow.
(At this point a number of tubes of litmus broth were
planted with saliva from various members of the class. In
planting tube marked No. 8 the platinum wire was not
passed entirely into the mouth, but was simply drawn be-
tween the closed lips in front of the teeth.)
I have marked two tubes ''control." These I will keep
with the rest under like conditions but without planting.
The result that we expect to get is the changing of the
color of the litmus from blue to red by the growth of micro-
organisms and the development of acid.

Hypersensitive Dentin, Continued.
Wben I stopped on Monday I was speaking of sensi-

tive dentin, dentin that had become sensitive on account
of invasion by caries. You will remember that I explained
how it was that dentin may be sensitive, yet having no
nerves. The fibrils of Tomes being projections of the sub-
stance of the odontoblasts through the dentin to the enamel
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