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. Such injections belong to
the simplest and surest means of producing suppurations free from
living bacteria.

Tuberculous guinea pigs, on the other hand, are killed by the
injection of very small quantities of such diluted cultivations. In
fact, within six to forty-eight hours, according to the strength of
the dose, an injection which is not sufficient to produce the death of
the animal may cause extended necrosis to the skin in the vicinity of
the place of injection. If the dilution is still further diluted until
it is scarcely visibly clouded, the animals inoculated remain alive
and a noticeable improvement in their condition soon supervenes. If
the injections are continued at intervals of from one to two days, the
ulcerating inoculation wound becomes smaller and finally scars over,
which otherwise it never does; the size of the swollen lymphatic
glands is reduced, the body becomes better nourished, and the morbid
process ceases, unless it has gone too far, in which case the animal
perishes from exhaustion. By this means the basis of a curative
process against tuberculosis was established.

Against the practical application of such dilutions of dead tubercle
bacilli there presented itself the fact that the tubercle bacilli are