The great enemy of books is unquestionably damp, which corrodes the paper, covering it with reddish brown spots, or, in extreme cases, patches. These unsightly marks, if once they have taken a firm hold, cannot be removed, and the most that can be hoped for is some preventive against an aggravation of the evil. Damp, unlike mere surface stains, attacks the tissue of the paper, rotting it completely through, and not infrequently destroying it altogether. It is like a vital disease which insinuates itself into the very seat of life, and, with more or less despatch, consumes its victim. Unslaked lime, as is well known, has a strong affinity for moisture of every kind, and when there is plenty of this substance about, damp is irresistibly attracted to it. Small saucers full of lime should therefore be placed in close proximity to valuable books, on the shelves if necessary, but never in immediate contact with the books themselves, or the remedy will be as bad as the disease to be guarded against. The action of lime upon moisture has been very well known for centuries, yet no one seems to have thought of applying it to this useful purpose, and books have been doomed to slow but sure destruction for the want of a precaution as simple as it is obvious. Only the other day a correspondent, writing to an American bibliographical journal, pointed out what he called a new remedy against damp, which turned out to be based upon nothing else than the well-known relationship which exists between lime and water. If damp has only just commenced its attack, the part affected should first be touched with a wash of spirits of wine, and when dry with a very weak solution of oxalic acid. If the "fox spots," as they are called, do not then disappear, the injury is permanent and no remedy exists, as far as we at present know. A really valuable book which stands in need of a thorough cleaning should be placed in the hands of some competent person, as considerable experience is necessary before even a reasonable degree of success can be assured. If the marks to be obliterated are numerous, the book had better be taken to pieces by removing the cover and separating the leaves, first cutting the binder's threads and taking especial care not to _tear_ anything. Each leaf must then be examined, both on the flat and when held up to the light, for it is essential that the particular description of dirt should be identified as closely as possible.