It is advised that water to be filtered should be well stirred with powdered alum added in small amount (two grains to a gallon, or one-quarter of an ounce to fifty gallons), and this poured through the filter pipe. Such precautions, and even boiling of water before filtering, are worthy of thought, not only when any wide-spread epidemic prevails, but also when there is any good reason to suspect impurity of water supply. Where there is the least suspicion of the well water, it is best first to consult the family physician, who may aid in the more simple tests; but if there is good reason for suspicion, he will advise you not wholly to rely upon these approximate results, but direct you to those who have more experience in the work and the advantages of laboratories with all appliances needed.—Sel.