lace the mouth at the illuminated focus of the electric
beam and inhale the thickly-massed dust revealed there. Nor is the
repugnance abolished by the reflection that, although we do not see the
floating particles, we are taking them into our lungs every hour and
minute of our lives." "The notion was expressed by Kircher and favored
by Linnaeus, that epidemic diseases are due to germs which float in the
atmosphere, enter the body, and produce disturbance by the development
within the body of parasitic life. While it was struggling against great
odds, this theory found an expounder and a defender in the President of
this institution. At a time when most of his medical brethren considered
it a wild dream, Sir Henry Holland contended that some form of the
germ-theory was probably true." Professor Tyndall proposes means by the
application of which air loaded with noxious particles may be freed from
them before entering the air passages. The following embodies his
suggestions on this point:

COTTON-WOOL RESPIRATOR.

"I now empty my lungs as perfectly as possible, and placing a handful of
cotton-wool against my mouth and nostrils, inhale through it. There is
no difficulty in thus filling the lungs with air. On expiring this air
through a glass tube, its freedom from floating matter is at once
manifest. From the very beginning of the act of expiration the beam is
pierced by a black aperture. The first puff from the lungs abolishes the
illuminated dust, and puts a patch of darkness in its place; and the
darkness continues throughout the entire course of the expiration. When
the tube is placed below the beam and moved to and fro, the same
smoke-like appearance as that obtained with a flame is observed. _In
short, the cotton-wool, when used in sufficient quantity, and with due
care, completely intercepts the floating matter on its way to the
lungs_.

The application of these experiments is obvious. If a physician wishes
to hold back from the lungs of his patient, or from his own, the germs
or virus by which contagious disease is propagated, he will employ a
cotton-wool respirator. If perfectly filtered, attendants may breathe
the air unharmed. In all probability the protection of the lungs and
mouth will be the protection of the entire system. For it is exceedingly
probable that the germs which lodge in the air-passages, or find their
way with the saliva into the stomach with its absorbent system, are
those which sow in th