Mildew in Books

Can you, or any of your readers, suggest a preventive for mildew in books? In a valuable public library in this town (Liverpool), much injury has been occasioned by mildew, the operations of which appear very capricious; in some cases attacking the printed part of an engraving, leaving the margin unaffected; in others attacking the inside of the backs *only*; and in a few instances it attacks all parts with the utmost impartiality. Any hints as to cause or remedy will be most acceptable.