sample of dust be collected and carefully ignited, the organic matter will be burned away and any ammonium salts volatilized, while the mineral portion will be unacted upon; and in this way it has been shown that more than one half of the suspended matters in the air are of organic origin, a large portion of this organic matter consisting of germs which are capable of setting up fermentation, disease, and decay.
It is only within the last few years that the importance of the work done by the solid particles of dust floating in the air has been recognized, and it is to Pasteur that we owe the knowledge that these germs set up the various processes of organic decay, by which the waste matter derived from vegetable sources is once again resolved into the water vapor and carbon dioxide used by Nature as the foundation of all organic creations. It is the almost imperceptible germs floating in the air which start this marvelous natural action—germs so minute that it requires the strongest microscope to detect them, yet so potent that the whole balance of life hangs on their existence. These facts show us that not only has dust a most marvelous history, but that in it Nature has disguised her most important factor for cleaning the face of the earth from waste matter of both mineral and vegetable origin.
The surface soil when mixed with water gives the mud which dirties our boots, and forms clots on the train of our skirts; but this, as well as the dust which has settled in our living rooms, and merely clings mechanically to the surfaces upon which it has deposited, may be removed by such simple physical means as the duster and brush. When dust has found its way into a fabric such as a carpet, it requires considerable force to again dislodge it, and this is applied by means of the broom; but in vigorous sweeping we find that the largest proportion of the dust is driven up into the air, only to resettle once again on other surfaces, so that although we can make the nuisance "move on," we do not in this way remove it, and experience has taught our servants that wet tea-leaves scattered on the carpet before sweeping lessen this evil. In some cases, instead of using this method, it has been argued that it must be the moisture which acts in preventing the raising of the dust, and the carpet has been sprinkled with water. This converts the dust into mud, which remains fixed in the fabric while the sweeping is going on, but as soon as the water has evaporated from it, again reasserts its right of rising as dust.
When, however, wet tea-leaves, damp sawdust, or even moistened sand is scattered over the surface to be swept, the dust when dislodged adheres to the moistened substance and is removed. In choosing moist bodies for this purpose, the only points to consider are that they must have no staining action on the carpet, must not be too wet, and must not be so finely grained as to
