means of conveying malarial poisons to places at a distance," by distributing organic matter held in suspension. Dr. Edwards, of Montreal, found two grains of organic matter to the gallon of melted shore-ice, and one grain to the gallon of river-ice. One writer, Pavy, says, "River water and the water of shallow wells should always be regarded with suspicion," and he adds, "There is evidence to show that the most serious consequences have arisen from the consumption of impure water." Buck, in "Hygiene and Public Health," says, "The weight of evidence and authority favors the idea that the drinking-water may become the cause of disease, and in drinking a polluted water one always runs more or less risk." The River Pollution Commission of London, after analyzing water from different sources, reported dangerous "river-water to which sewage gains access."
The conclusion from the above quotations is, not that one should abstain from drinking water on account of the difficulty in obtaining it pure, but that proper precautions should be observed to obtain it pure. Water is Nature's means of slaking thirst, and with its refreshing properties combines valuable therapeutic qualities.
An excellent article, published in the "Boston Journal of Chemistry," in treating of the curative value of water says: "We notice the salutary influence of water-drinking upon many of those who resort to the so-called mineral springs which abound in the country. It is not necessary that these springs should hold abnormal quantities of salts of any kind to effect cures; it is only necessary that the water should be pure. Ordinary springs, such as are found in every farmer's pasture, are curative springs if the waters are used freely by those who suffer from certain gastric or renal difficulties." This writer asserts that the best known of our Eastern mineral waters shows, on analysis, that its curative value consists solely in its purity.
It may be truthfully asserted that it is impossible to procure perfectly pure water. "Even distilled water and fresh rain-water contain some ammonia, carbonic acid, and other matters which detract from their purity; while the best water from rivers, wells, ponds, and tanks, contains a large number of chemical compounds, chiefly salts." The skillful use of the microscope would condemn the water from many sources for drinking purposes which now is considered pure. But while we can not obtain strictly pure water, even by distillation, we can obtain it so pure that it will meet our demands, and that without danger to the consumer's health. The means by which this may be accomplished is filtration.
A filter is an apparatus for separating from fluids the foreign substances mechanically intermixed with them and held in suspension. While this is all that most filters aim to accomplish, yet experiments show that a filtering material may be used which very markedly diminishes the foreign bodies usually held in solution in water, and also removes those held in suspension.
