Cork is produced from the thick bark of the cork oak (Quercus suber). It is harvested from the living trees about once every ten years in an environmentally sustainable industry.[116] More than half the world's cork comes from Portugal and is largely used to make stoppers for wine bottles.[117] Other uses include floor tiles, bulletin boards, balls, footwear, cigarette tips, packaging, insulation and joints in woodwind instruments.[117] The bark of other varieties of oak has traditionally been used in Europe for the tanning of hides though bark from other species of tree has been used elsewhere. The active ingredient, tannin, is extracted and after various preliminary treatments, the skins are immersed in a series of vats containing solutions in increasing concentrations. The tannin causes the hide to become supple, less affected by water and more resistant to bacterial attack.[118] The commonly used spice Cinnamon is obtained from the bark from a number of species of the genus Cinnamomum[119] At least a hundred and twenty drugs come from plant sources, many of them from the bark of trees.[120] Quinine originates from the cinchona tree (Cinchona) and was for a long time the remedy of choice for the treatment of malaria.[121] Aspirin was synthesized to replace the sodium salicylate derived from the bark of willow trees (Salix) which had unpleasant side effects.[122] The anti-cancer drug Paclitaxel is derived from taxol, a substance found in the bark of the Pacific yew (Taxus brevifolia).[123] Other tree based drugs come from the paw-paw (Carica papaya), the cassia (Cassia spp.), the cocoa tree (Theobroma cacao), the tree of life (Camptotheca acuminata) and the downy birch (Betula pubescens).[120] The papery bark of the white birch tree (Betula papyrifera) was used extensively by Native Americans. Wigwams were covered by it and canoes were constructed from it. Other uses included food containers, hunting and fishing equip ent, musical instruments, toys and sledges.[124] Nowadays, bark chips, a by-product of the timber industry, are used as a mulch and as a growing medium for epiphytic plants that need a soil-free compost. Tanning is the process of treating skins of animals to produce leather, which is more durable and less susceptible to decomposition. Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name (tannin is in turn named for an old German word for oak or fir trees, which supplied it). Coloring may occur during tanning. A tannery is the term for a place where the skins are processed. Tanning leather involves a process which permanently alters the protein structure of skin. Making "rawhide" (untanned but worked hide) does not require the use of tannin. Rawhide is made by removing the flesh and fat and then the hair by use of an aqueous solution (this process is often called "liming" when using lime and water or "bucking" when using wood ash (lye) and water), then scraping over a beam with a somewhat dull knife, then drying. The two aforementioned solutions for removing the hair also act to clean the fiber network of the skin and allow penetration and action of the tanning agent, so that all the steps in preparation of rawhide except drying are often preludes to the more complex process of tanning and production of leather. Tanning can be performed with either vegetable or mineral methods. Before tanning, the skins are unhaired, degreased, desalted and soaked in water over a period of 6 hours to 2 days. To prevent damage of the skin by bacterial growth during the soaking period, biocides, typically dithiocarbamates, are used. Fungicides such as TCMBT, 2-(Thiocyanomethylthio) benzothiazole, are added later in the process to protect wet leathers from mould growth. After 1980 the use of pentachlorophenol and quicksilver (mercury base) biocides and their derivatives was forbidden.