, from Aristotle and Lucretius downward. Such a one may have
a just claim to be considered a man of learning, and far be it from me to
despise the branches of knowledge toward which his mind has a natural
bent. But in so far as his knowledge is a knowledge of fancies rather
than facts, it has no claim to be called science.

Fancies, however beautiful, cannot form a solid basis for action or
conduct, whereas a scientific fact does. It is all very well to suppose
that such and such things may be, but mere possibilities, or even
probabilities, do not breed a living faith. They often foster schism, and
give rise to disunited or opposed action on the part of those who think
that such and such things may not be.

When, however, a fancy or a speculation becomes a fact which is capable
of demonstration, its universal acceptance is only a matter of time, and
the man who neglects such facts in regulating his actions or conduct is
rightly regarded as insane all the world over.

The influence of micro-organisms on disease is emerging more and more,
day by day, from the regions of uncertainty, and what once were the
speculations of the few are now the accepted facts of the majority.

Miquel's experiments show very clearly that the number of microbes in the
air corresponds with tolerable closeness to the density of population.
From the Alpine solitudes of the Bernese Oberland to the crowded ward of
a Parisian hospital, we have a constantly ascending ratio of microbes in
the air, from zero to 28,000 per cubic meter. Their complete absence on
the Alps is mainly due to the absence of productive foci. Organic matter
capable of nourishing microbes is rare, and the dryness and cold prevent
any manifestation of vitality or increase. Whence come the large number
of microbes in the crowded places and in hospitals?

Every individual, even in health, is a productive focus for microbes;
they are found in the breath, and flourish luxuriantly in the mouth of
those especially who are negligent in the use of the tooth brush. When we
speak of "flourishing luxuriantly," what do we mean? Simply that these
microbes, under favorable circumstances, increase by simple division, and
that one becomes about 16,000,000 in twenty-four hours.

The breath, even of healthy persons, contains ammonia and organic matter
which we can smell. When the moisture of the breath is condensed and
collected, it will putrefy. Every drop of condensed moisture that forms
on