h a nature that a
single attack may suffice to ruin the constitution for life. Collective or
_racial acclimation_ certainly existed in the past, at a time when
specific remedies for pernicious malaria were unknown; and even later,
when the employment of these remedies was very limited. The acclimation
was due to a natural selection made by the malaria upon successive
generations, from which it took away, almost without opposition, all those
who possessed but a feeble individual power of resistance to the specific
poison, while it spared those who possessed this power of resistance in an
extraordinary degree. The first were, according to the Grecian myth, _the
human victims destined to appease the monster or demon who opposed the
violation of the territory over which he had up to that time exercised an
absolute sovereignty_. The second became the founders of the race, and
through them, from generation to generation, the collective power of
resistance to the malaria was progressively increased. In our own days a
like selection may take place among barbarous races, as it does among the
cattle and the horses in a malarious region, but it has become an
impossibility among civilized nations. By means of the specific remedies
which we possess, the use of which is now so general, the lives of a large
number of individuals whose resisting powers are very feeble are
preserved; and these individuals beget others whose power of resistance to
the action of the specific poison is still more feeble. This results after
a number of generations in the physical degradation of that part of the
human race which inhabits malarious countries.

We cannot, therefore, in the future, count upon the assistance of external
natural forces to increase the power of resistance of human society
against the assaults of malaria. Such an object can be obtained only by
artificial means. It has been sought to attain this end by the daily
administration of the salts of quinine, of the salicylates, and of the
tincture of eucalyptus, each and every one tried in turn. But the salts of
quinine are dear, exercise a prompt, though very transient anti-malarial
action, and, when administered for a long time, disturb rather seriously
the functions of the digestive and nervous systems. The salicylates, when
well prepared, are rather dear, and there is as yet no proof that they
possess prophylactic powers against malaria. The alcoholic tincture of
eucalyptus is useful in