Page 207 - My FlipBook

margins of the filling are the vulnerable lines, and these we
must devise means of making tight enough so that
acid may not seep in between the filling and the margins of
the cavity.

February 28.
I promised the class yesterday that I would exhibit this
morning the tubes of litmus broth that were planted with
saliva to illustrate the manner in which the saliva in the mouth
becomes acid by the growth of micro-organisms. I have the
tubes here. They were placed in the incubator, which is kept
at the temperature of the body, within an hour after planting
and have remained at that temperature until a few minutes
ago.
In all of the tubes planted the litmus has become reddened
by the development of acid, except one, and you will note also
that there is a considerable growth of micro-organisms in
each. In all of them the broth has become cloudy and there
are flocculent masses of micro-organisms distributed through
it. You will remember that there was some question yester-
day whether or not I had planted tube No. 6, and that I said
I could tell you certainly this morning. It is now clear that
it was not planted, for it has no growth and the litmus re-
mains blue. You will notice that the controls also remain
blue. I will distribute these in trays, two red and two blue
tubes in each, and pass them for your examination (passes the

trays among the members of the class).
You will also remember that tube No. 8 was planted by
simply drawing the platinum wire between the lips in front
of the teeth without passing it into the mouth. It has grown
and the litmus has been reddened the same as the others. This
illustrates the fact that every time you touch your fingers to
the lips of your patient, or to your own. you infect them with
micro-organisms. You never know just what kind, whether
pathogenic or non-pathogenic. It also illustrates the fact
that your operating instruments are always infected when you
use them in the mouth of any patient.
The principal point, however, in this particular exhibit is
to illustrate the manner in which the saliva is rendered acid
l)y the growth of micro-organisms in it. This has been suffi-
ciently explained in a previous lecture.

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