Page 84 - My FlipBook

micro-organisms by boiling, and if we get these spores
started once we are sure to destroy them we cannot safely
;
sterilize otherwise. For our purposes, cultivating micro-or-
ganisms from the mouth that form acids, we add a little bit
of sugar to the broth, for we find that those micro-organ-
isms that form lactic acid will not form the acid without sugar
or starch or some of the hydrocarbons of that order
I have here some specimens of agar agar that I may
pass among you. This is made by taking the gelatin from
Irish moss and mixing enough of it with the broth to form
a compound that will be stif¥ when cold. This will melt
down at about 120 degrees. It has an advantage over gelatin
in that we can use the body temperature in the cultivation of
micro-organisms in it. That is a very clear, nice specimen of
agar agar. (Passes it to the class.) There are several things
to be gained in the use of agar agar instead of animal gelatin.
Here I have some tubes of animal gelatin ; some of them
have not been laid, some of them have been laid. (Passes
them to the class.) This is made by placing ordinary glue
or animal gelatin in this broth until it makes a compound
that is stifT enough to stand at a temperature of 75 to 80
degrees Fahr. None of these that I show you have been
planted. I may say that in a box of fifty tubes from Parke
Davis & Co., that I have just opened, I found twenty-three
of them contained mold we lost that number. Of two flasks
;
of broth, one came with micro-organisms growing in it. It
is a little bit discouraging. I have lost more than half the
material I bought from them. Through some carelessness
in putting them up they have molds or micro-organisms, and
it illustrates to you something of the extreme care that is
necessary in the preparation of this culture media ; any little
mistake and it is gone. Micro-organisms get in and begin
their growth.
Now we will plant some of this media and I will show

you the results at our next lecture. We will plant direct
from the mouth. I have a platinum needle here with a little
loop on the end of it. It is not necessary to have a loop.
The plain, smooth, straight platinum wire will an-
swer the purpose, for when we put that in the mouth
and take it out ever so carefully, or even draw it
between the lips, it will be infected, and placing it in the broth

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