Each of these substances seems to have come into use independently, in
widely separated countries, to produce the same effects, namely, to
refresh, renew, or sustain the physical and mental organism, and it was a
curious surprise to find, after they had all been thus long used, that
although each came from a different natural order of plants, the same
active principle--namely, caffeine--could be extracted in different
proportions from all. It is now still more curious, however, to find that
for centuries another plant, namely coca, yielding a different principle,
has been in use for similar purposes, the effects of which differ as
little from those of tea, coffee, etc., as these do among themselves. Yet
cocaine is chemically very different from caffeine, simply producing a
similar physiological effect in much smaller doses. All these substances
in their natural condition seem to be identical in their general
physiological effect, but idiosyncrasy, or different individual
impressibility or sensitiveness, causes a different action, as well in
quality as in degree from the different substances, upon some persons.
In order to throw a little additional light on the comparative activity
of the principal individuals of this group of substances, the following
trials were made.
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