This is our second culture. This must be repeated until we are
satisfied that we have secured a _pure_ culture. If this be carried to
the twenty-fifth generation, we may be assured that there remains no
pus, no ptomaines, nothing but the desired bacilli.
It is a proper material now for inoculation, and if we inoculate some
of the lower animals, for instance the monkey, we produce a disease
identical with phthisis pulmpnalis. Bacteria also afford peculiar
chemical reactions. For example, nitric acid will discharge all the
color from all bacilli artificially dyed with anilin, except those of
tubercle and anthrax. One species is stained readily with a dye that
leaves another unaltered. Thus we are enabled in the laboratory to
determine whether the bacilli found in sputum, for example, are from
tubercle or are the bacteria of decomposition.
From what I have said of the tubercle bacillus, it would seem
thoroughly demonstrated that it is the cause of tubercle in these
animals. But we must walk cautiously here. These are not human beings,
who know that like results would follow their inoculation. The animals
used by Koch are animals very subject to tubercle.
We must, from the very nature of our environment, be constantly
inhaling these germs as we pass through the wards of our hospitals;
yes, they are floating in the air of our streets and dwellings.
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