solve the problem of the prevention of disease. There was much that was
still obscure in this very intricate problem, but the new light which
was daily being thrown upon the causes of disease by the careful and
exact researches of the chemist and physiologist was gradually tending
to explain those causes and to raise the science of hygiene, or science
of prevention of disease, out of the region of speculation, and enable
it to take rank as one of the exact sciences. Long ago the careful
observation of facts had shown that the preservation of health required
certain conditions to be observed in and around dwellings, conditions
which, when neglected, had led to the outbreaks of epidemic disease from
the days of Moses to the present time. But while the results had been
patent, it was only in recent years that a clew had been obtained to the
occult conditions in air and water to enable their comparative healthful
purity to be distinguished.

The researches of Pasteur in respect to the forms of disease in French
vineyards opened a fruitful field of inquiry, and the theories of Dr.
Bastian on spontaneous generation gave rise to the beautiful series
of experiments by Tyndall on bacterian life. A large band of leading
scientific men, both in this country and over the whole world, were
devoting their energies to a knowledge of the recent theories on the
propagation of disease by germs. In a lecture on fermentation, Tyndall
remarked that the researches, by means of which science has recently
elucidated the causes of fermentation, have raised the art of brewing
from being an art founded on empirical observation--that is to say,
on the observation of facts apart from the principles which explain
them--into what may be termed an exact science.

In like manner, if recent theories on the propagation of disease by
germs were proved to be correct, and if the laws which govern the