Page 94 - My FlipBook

ing up bits for replanting into other tubes. This needle I will
sterilize as before. I will say that it is uncertain planting in
such a place as this, because I am handling other things
more or less and I am liable to get the spores of mold onto
my fingers and get them into the tubes. It requires a great
deal of care to plant and obtain pure growths with certainty.
I passed some examples of these tubes of agar agar and gela-
tin among you on Monday. These we heat until they are
soft, lay them down in a slanting position and allow them to
cool in that position in order to get a broader surface on
which to plant. The planting is done in a similar manner to
the planting which you saw on Monday, though we generally
turn these tubes bottom side up in order to be more certain
to prevent molds and other germs from falHng into them.
(Passes the sterilized needle into the mouth of one of the
students.) I will prick this agar agar in a number of places
and then run it clear through the material. (Plants tube No.
I.) Now these do not grow so rapidly as in broth. We will
see what growth that will make by next Monday.
Here is a tube I just noticed. Through some careless-
ness I have brought along a tube that has a little mold in it.
I will pass it among you. Of course, it is not fit for planting.
It is one of the tubes of the lot that I spoke of Monday.
(Passes tube to class.) This is one of the ordinary house
molds, penicillium niger.
(Plants tube No. 2.) Now we will see if we can get a
growth from that. I want you to notice particularly that I
send that needle through the agar agar to the bottom of the
tube, and look for the track of that needle after it has grown.
I will say that there are now in the museum eight or ten
tubes with these growths that I planted before the class from
saliva, and one or two pure growths that I planted in the
laboratory last year. You can see by examining them how
they have kept. They were planted on agar agar the same
as I am planting these.
(Plants tube No. 3.) Now I have here some tubes of
gelatin. Not liking to plant these when they are cold and
stiff, I put them in the incubator to warm up a little. They
were in the incubator at 98 degrees for about twenty min-
utes. I find they have stood a little too long; one has be-
come soft and has run a little, but it is hard in its new posi-

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