Lignum nephriticum

Lignum nephriticum (Latin for "kidney wood") is a traditional diuretic that was derived from the wood of two tree species, the narra (Pterocarpus indicus) and the Mexican kidneywood (Eysenhardtia polystachya ). The wood is capable of turning the color of water it comes in contact with into beautiful opalescent hues that change depending on light and angle, the earliest known record of the phenomenon of fluorescence. Due to this strange property, it became well known in Europe from the 16th to the early 18th-century Europe. Cups made from lignum nephriticum were given as gifts to royalty. Water drunk from such cups, as well as imported powders and extracts from lignum nephriticum, were thought to have great medicinal properties.

The lignum nephriticum derived from Mexican kidneywood was known as the coatli, coatl, or cuatl ("snake water") or tlapalezpatli ("blood-tincture medicine") in the Nahuatl language. It was traditionally used by the Aztec people as a diuretic prior to European contact. Similarly, the lignum nephriticum cups made from narra wood were part of the native industry of the Philippines before the arrival of the Spanish. The cups were manufactured in southern Luzon, particularly in the Naga region. The name of which was derived from the abundance of the narra trees, which was known as in the Bikol language (literally "serpent" or "dragon").

The first known description of the medicine appears in the Historia general de las cosas de la Nueva España (1560–1564) by the Spanish Franciscan missionary and ethnographer Bernardino de Sahagún. In the most famous surviving manuscripts of the work, the Florentine Codex, Sahagún called it by its Nahuatl name, coatli, given by Aztec healers. He described its unusual property of turning the color of water that comes in contact with it to bright blue: "...patli, yoan aqujxtiloni, matlatic iniayo axixpatli [...it is a medicine, and makes the water of blue color, its juice is medicinal for the urine]".

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