Vegetable Fluids.—­Many roots exist, from which both natives and animals obtain a sufficiency of sap and pulp, to take the place of water.  The traveller should inquire of the natives, and otherwise acquaint himself with those peculiar to the country that he visits; such as the roots which the eland eats, the bitter water-melon, etc.

To purify water that is muddy or putrid.—­With muddy water, the remedy is to filter, and to use alum, if you have it.  With putrid, to boil, to mix with charcoal, or expose to the sun and air; or what is best, to use all three methods at the same time.  When the water is salt or brackish, nothing avails but distillation. (See Distilled Water,” p. 218.)

To filter Muddy Water.—­When, at the watering-place, there is little else but a mess of mud and filth, take a good handful of grass or rushes, and tie it roughly together in the form of a cone, 6 or 8 inches long; then dipping the broad end into the puddle, and turning it up, a streamlet of fluid will trickle down through the small end.  This excellent plan is used by the Northern Bushmen—­at their wells quantities of these bundles are found lying about. (Anderson.) Otherwise suck water through your handkerchief by putting it over the mouth of your mug, or by throwing it on the gritty mess as it lies in the puddle.  For obtaining a copious supply, the most perfect plan, if you have means, is to bore a cask full of auger holes, and put another small one, that has had the bottom knocked out, inside it; and then to fill the space between the two, with grass, moss, etc.  Sink the whole in the midst of the pond; the water will run through the auger-holes, filter through the moss, and rise in the inner cask clear of weeds and sand.  If you have only a single cask, holes may be bored in the lower part of its sides, and alternate layers of sand and grass thrown in, till they cover the holes; through these layers, the water will strain.  Or any coarse bag, kept open with hoops made on the spot, may be moored in the mud, by placing a heavy stone inside; it will act on The same principle, but less efficiently than the casks.  Sand, charcoal, sponge, and wood, are the substances most commonly used in properly constructed filters:  peat charcoal is excellent.  Charcoal acts not only as a mechanical filter for solid impurities, but it has the further advantage of absorbing putrid gases.  (See below, “Putrid Water.”) Snow is also used as a filter in the Arctic regions.  Dr. Rae used to lay it on the water, until it was considerably higher than its level, and then to suck the water through the snow.

Alum.—­Turbid water is also, in some way as yet insufficiently explained, made clear by the Indian plan of putting a piece of alum into it.  The alum appears to unite with the mud, and to form a clayey deposit.  Independently of the action, it has an astringent effect upon organic matters:  it hardens them, and they subside to the bottom of the vessel instead of being diffused in a glairy, viscous state, throughout the water.  No taste of alum remains in the water, unless it has been used in great excess.  Three thimblefuls of alum will clarify a bucketful of turbid water.