k-jaw, and snake-bite) is an
attempt to bring to the rescue of a patient who would sooner or later
produce his own antitoxins (but perhaps too late or in insufficient
quantity) the similar antitoxin obtained from the blood of another
animal which has been artificially made to produce in its blood an
excessive quantity of that substance.

Mithridates, King of Pontus, was, according to ancient legend, in
consequence of his studies and experiments, soaked with all kinds of
poisons to which he had become habituated by gradually increasing
doses, and he had at last reached a condition in which no poison could
harm him, so that when he was captured by the Romans and wished to
kill himself (which was the correct thing in those days for a fallen
king to do), he wept because he was unable to get any poisons which
would act upon him. He was "immune" to all poisons. This real or
supposed immunity resulting from the introduction into the living body
at intervals of a series of doses of a poison gradually increasing
strength has been called "Mithridatism," and animals and men so
treated have been said to be "mithradatized." The toleration of
poisonous drugs--such as tobacco and alcohol, and even of mineral
poisons, such as arsenic--was, until lately, regarded as merely a
special exhibition of that habituation of "adaptation by use" which
living things often show in regard to some of the conditions of their
life. Unusual cold, unusual heat, unusual moisture, salinity or the
reverse, unusual deprivation of food, unusual muscular effort may be
tolerated by animals without injury provided that they have been
"gradually accustomed" to the unusual thing, or, in other words, that
the unusual has been gradually made the usual; so that there is a
saying that eels after a time even get used to being skinned. There
was no attempt to explain the details of this process of habituation;
it was assumed to be a part of the general "educability" of living
matter.

The study of the education of living matter, in regard to various
conditions which can act upon it, has yet to be further carried out,
but the way in which the poisons made by disease germs and the like,
and the disease germs themselves, are dealt with in the blood and
tissues has, on account of its urgent importance, from a medical point
of view, been already profoundly studied by experimental and
microscopic methods of late years. The old notion as to "mithridatism"
was that an animal