“…Chemical investigations of the medicinal hypothesis have focused mainly on the consequences of two types of non-nutritional ingestion (i.e., ingestion of items that appear to be of little or no nutritive significance) in chimpanzees: 1) swallowing whole leaves of various species, and 2) ingesting the bitter pith of Vernonia amygdalina [Huffman & Seifu, 1989;Wrangham & Goodall, 1989;Wrangham & Nishida, 1983]. The antiparasitic properties of the plants ingested by chimpanzees in these cases were also investigated [Huffman et al, , 1996bKoshimizu et al, 1994;Jisaka et al, 1992Jisaka et al, , 1993Ohigashi et al, 1994]. While leaf-swallowing has been convincingly implicated as an agent of parasite expulsion [Huffman & Caton, 2001;Huffman et al, 1996b], and may be involved in alleviating digestive pain caused by parasites [Wrangham, 1995], its known effects are due to physical rather than chemical causes [Huffman & Caton, 2001;Huffman et al, 1996a;1997;Page et al, 1997].…”