Opinions are so firmly fixed at present that water is capable of carrying the germs of disease that, in cases of epidemics, the recommendation is made to drink natural mineral waters, or to boil ordinary water.  This is a wise measure, assuredly; but mineral waters are expensive, and, moreover, many persons cannot get used to them.  As for boiled water, that is a beverage which has no longer a normal composition; a portion of its salts has become precipitated, and its dissolved gases have been given off.  In spite of the aeration that it is afterward made to undergo, it preserves an insipid taste, and I believe that it is not very digestible.  I have thought, then, that it would be important, from a hygienic standpoint, to have a filter that should effectually rid water of all the microbes or germs that it contains, while at the same time preserving the salts or gases that it holds in solution.  I have reached such a result, and, although it is always delicate to speak of things that one has himself done, I think the question is too important to allow me to hold back my opinion in regard to the apparatus.  It is a question of general hygiene before which my own personality must disappear completely.

In Mr. Pasteur’s laboratory, we filter the liquids in which microbes have been cultivated, so as to separate them from the medium in which they exist.  For this purpose we employ a small unglazed porcelain tube that we have had especially constructed therefor.  The liquid traverses the porous sides of this under the influence of atmospheric pressure, since we cause a vacuum around the tube by means of an air-pump.  We collect in this way, after several hours, a few cubic 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.