If I were to
take a glass plate, one side of which is coated with a thick solution
of peptonized gelatin, and allow the water to collect, the gelatinous
matter will become solid. If now, with a wire dipped in some
tuberculous matter, I draw a line along the gelatin, I have deposited
at intervals along this line, specimens of tubercle bacilli. If this
plate be now kept at a proper temperature, after a few days, wherever
the bacilli have been caught, a grayish spot will appear, which,
easily seen with the naked eye, gradually spreads and becomes larger.
These spots are colonies containing thousands of bacilli. Let us
return to our gelatin plate.
We find a spot which answers to the description of a colony of
tubercle bacilli. We now take a minute particle from this colony on a
wire and convey it to the surface of some hardened blood serum in a
test tube. We plug the tube so that no air germs may drop in, and
place it in an incubator at the proper temperature. After several
days, if no contamination be present, a colony of bacilli will appear
around the spot where we sowed the spores. Let us repeat the process.
Take a particle from this colony, and transfer it to another tube.
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