ubic inches of a liquid which is absolutely
pure, since animals may be inoculated with it without danger to them, while
the smallest quantity of the same liquid, when not filtered, infallibly
causes death.

This is the process that I have applied to the filtration of water. I have
introduced into it merely such modifications as are necessary to render the
apparatus entirely practical. My apparatus consists of an unglazed
porcelain tube inverted upon a ring of enameled porcelain, forming a part
thereof, and provided with an aperture for the outflow of the liquid. This
tube is placed within a metallic one, which is directly attached to a cock
that is soldered to the service pipe. A nut at the base that can be
maneuvered by hand permits, through the intermedium of a rubber washer
resting upon the enameled ring, of the tube being hermetically closed.

Under these circumstances, when the cock is turned on, the water fills the
space between the two tubes and slowly filters, under the influence of
pressure, through the sides of the porous one, and is freed from all solid
matter, including the microbes and germs, that it contains. It flows out
thoroughly purified, through the lower aperture, into a vessel placed there
to receive it.

I have directly ascertained that water thus filtered is deprived of all its
germs. For this purpose I have added some of it (with the necessary
precautions against introducing foreign organisms) to very changeable
liquids, such as veal broth, blood, and milk, and have found that there was
no alteration. Such water, then, is incapable of transmitting the germs of
disease.

[Illustration: CHAMBERLAND'S WATER FILTER.]

With an apparatus like the one here figured, and in which the filtering
tube is eight inches in length by about one inch in diameter, about four
and a half gallons of water per day may be obtained when the pressure is
two atmospheres--the mean pressure in Mr. Pasteur's laboratory, where my
experiments were made. Naturally, the discharge is greater or less
according to the pressure. A discharge of three and a half to four and a
half gallons of water seems to me to be sufficient for the needs of an
ordinary household. For schools, hospitals, barracks, etc., it is easy to
obtain the necessary volume of water by associating the tubes in series.
The discharge will be multiplied by the number of tubes.

In the country, or in towns that have no water mains, it will be easy to
devise an a