Page 103 - My FlipBook

NINTH LECTURE.

Exhibition of Micro-organisms.

I have brought with me this morning the tubes planted
in broth. Most of them have fallen down and the broth has
become nearly clear. There are a few of them that contain
certain micro-organisms that do not drop down readily, and
are not quite clear. Some of them have a few hanging to
the sides. You will see that the two tubes at the end here
remain clear. They were the control tubes that were not
planted, and they have been subjected to the same condi-
tions precisely that the others have. The one with the litmus
is almost as clear as the others; it has a little reddish cast;
the litmus has been destroyed. There are some of the micro-
organisms that decompose litmus and destroy the color. -
(Passes tubes to class.)
The plants on gelatin and agar-agar have all grown.
You will remember that the needle was thrust through the
agar-agar to the bottom of the tube. Look for the track
of the needle and you will find that the micro-organisms have
grown throughout its length, illustrating how it is that you
carry micro-organisms into a root-canal and through a root-
canal into the tissues beyond on a broach, if the broach is
infected, and the necessity for having broaches that are
clean—surgically clean. When we say surgically clean w^e
mean that they shall be free from micro-organisms. You
may prick the tissues with a rusty wire and it is not likely
to do much harm if it contains no micro-organisms. The
presence of micro-organisms is the dangerous element.
Those planted in gelatin that was cooled while the tubes
were upright, you will remember, the needle was simply
pricked through from top to bottom. You wall find micro-
organisms growing in the whole track of the needle, show-
ing a broad line of small white colonies, illustrating again
how they are carried by a needle prick. I have also put in
two others here that I had planted previously. You will
notice that the growth is very much slighter within the
depths of the media than it is when planted upon the sur-
face. Most of these organisms grow more rapidly when

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