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64 THE MICRO-ORGANISMS OF THE HUMAN MOUTH. :
ceed in exactly the same manner, except that the cultures must
be kept at a temperature just below that at which the gelatine
used liquefies. Instead of the ordinary glass plates, Petri'sche
Schalen may often be used to great advantage.
Dilution Ctdturcs.
"We may illustrate the principle of dilution cultures in the fol-
lowing manner : Suppose we have a handful of seeds of various
kinds which are invisible to the naked eye, and we are given the
task to separate the seeds, or at least to obtain pure cultures of
Fjo. 1G.
Second Dilution of a Gelatine-Culture from the White
Deposit on the Teeth.
a, very small ; h, medium-sized c, very large, round colonies
;
rf, irregular colony. The different sizes represent different
rapidities of growth. Culture three days old.
them. "We may accomplish the task in the following manner
We go out to the field and cast the seed broadcast upon the
ground which has been prepared for the sowing, wait till they
spring up and ripen, then gather the difl:erent plants which are
produced into separate heaps. In this way we obtain pure cul-
tures of all the diiferent plants represented in the original hand-
ful of invisible seeds.
In applying this principle to the pure cultivation of micro-
organisms we proceed as follows : Having melted three tubes
64 THE MICRO-ORGANISMS OF THE HUMAN MOUTH. :
ceed in exactly the same manner, except that the cultures must
be kept at a temperature just below that at which the gelatine
used liquefies. Instead of the ordinary glass plates, Petri'sche
Schalen may often be used to great advantage.
Dilution Ctdturcs.
"We may illustrate the principle of dilution cultures in the fol-
lowing manner : Suppose we have a handful of seeds of various
kinds which are invisible to the naked eye, and we are given the
task to separate the seeds, or at least to obtain pure cultures of
Fjo. 1G.
Second Dilution of a Gelatine-Culture from the White
Deposit on the Teeth.
a, very small ; h, medium-sized c, very large, round colonies
;
rf, irregular colony. The different sizes represent different
rapidities of growth. Culture three days old.
them. "We may accomplish the task in the following manner
We go out to the field and cast the seed broadcast upon the
ground which has been prepared for the sowing, wait till they
spring up and ripen, then gather the difl:erent plants which are
produced into separate heaps. In this way we obtain pure cul-
tures of all the diiferent plants represented in the original hand-
ful of invisible seeds.
In applying this principle to the pure cultivation of micro-
organisms we proceed as follows : Having melted three tubes
