A U. S. Forest Service film shows a forest's natural enemies: fire and destructive insects such as the spruce bark beetle. Mr. Mann further elaborates on the natural enemies of wood by including fungi, insects such as termites, and marine borers such as gribbles, and displays examples of damage done by each. He says that for wood preservatives to be useful, they must be poisonous to destructive organisms but not to humans or animals, permanent, non-corrosive, and inexpensive. He then discusses the chemicals in the creosote, oil-borne, and water-borne preservatives. Mr. Warnes compares the strength and fire retardation of treated and untreated wood and explains why treated wood is non-combustible. He further demonstrates a cylinder that pressure treats wood with preservative and notes that the primary markets for such wood are railroad crossties, poles, and crossarms; fenceposts and other farm-related uses; and housing. An industry film shows the detailed process of pressure creosoting large quantities of wood.