In such an animal the small indentation assumes the same
sticky covering at the beginning, but no nodules form. On the
contrary, on the day following, or the second day after the
inoculation, the place where the lymph is injected shows a strange
change. It becomes hard and assumes a darker coloring, which is not
confined to the inoculation spot, but spreads to the neighboring parts
until it attains a diameter of from 0.05 to 1 cm.
In a few days it becomes more and more manifest that the skin thus
changed is necrotic, finally falling off, leaving a flat ulceration
which usually heals rapidly and permanently without any involvement of
the adjacent lymphatic glands. Thus the injected tubercular bacilli
quite differently affect the skin of a healthy guinea pig from one
affected with tuberculosis. This effect is not exclusively produced
with living tubercular bacilli, but is also observed with the dead
bacilli, the result being the same whether, as I discovered by
experiments at the outset, the bacilli are killed by a somewhat
prolonged application of a low temperature or boiling heat or by means
of certain chemicals. This peculiar fact I followed up in all
directions, and this further result was obtained--that killed pure
cultivations of tubercular bacilli, after rinsing in water, might be
injected in great quantities under healthy guinea pig's skin without
anything occurring beyond local suppuration.
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