The ravages of worms and insects are among the principal causes of the destruction of timber. Some woods are more subject than others to be destroyed by them, such as alder, beech, birch, and in general all soft woods of which the juices are of a saccharine nature. Against the common worm, oil of spike is said to be an excellent remedy; and oil of juniper, or of turpentine, will prevent them in some degree. A free use of linseed oil is a good preservative, and so is a covering of copal varnish, but these can be applied to small articles only. Another application is sulphur which has been immersed in nitric acid and distilled to dryness, which, being exposed to the air, dissolves into an oil, the parts to be secured from the worm are to be anointed with this oil, which does not give an unpleasant odor to the wood. Lime is an excellent prevention against the worm, and sap-wood should always be impregnated with it when used in a dry situation. As worms do not attack bitter woods, soaking wood in an infusion of quassia has been tried, and is said to have the desired effect.