medicine and magic A major section of the Natural History, Books XX to XXIX, discusses matters related to medicine, especially plants that yield useful drugs. Pliny lists over 900 drugs, compared to 600 in Dioscorides's De Materia Medica, 550 in Theophrastus, and 650 in Galen. The poppy and opium are mentioned; Pliny notes that opium induces sleep and can be fatal. Diseases and their treatment are covered in book XXVI. Pliny addresses magic in Book XXX. He is critical of the Magi, attacking astrology, and suggesting that magic originated in medicine, creeping in by pretending to offer health. He names Zoroaster of Ancient Persia as the source of magical ideas. He states that Pythagoras, Empedocles, Democritus and Plato all travelled abroad to learn magic, remarking that it was surprising anyone accepted the doctrines they brought back, and that medicine (of Hippocrates) and magic (of Democritus) should have flourished simultaneously at the time of the Peloponnesian War. Agriculture The methods used to cultivate crops are described in Book XVIII. He praises Cato the Elder and his work De Agri Cultura, which he uses as a primary source. Pliny's work includes discussion of all known cultivated crops and vegetables, as well as herbs and remedies derived from them. He describes machines used in cultivation and processing the crops. For example, he describes a simple mechanical reaper that cut the ears of wheat and barley without the straw and was pushed by oxen (Book XVIII, chapter 72). It is depicted on a bas-relief found at Trier from the later Roman period. He also describes how grain is ground using a pestle, a hand-mill, or a mill driven by water wheels, as found in Roman water mills across the Empire. Metallurgy Pliny extensively discusses metals starting with gold and silver (Book XXXIII), and then the base metals copper, mercury, lead, tin and iron, as well as their many alloys such as electrum, bronze, pewter, and steel (Book XXXIV). He is critical of greed for gold, such as the absurdity of using the metal for coins in the early Republic. He gives examples of the way rulers proclaimed their prowess by exhibiting gold looted from their campaigns, such as that by Claudius after conquering Britain, and tells the stories of Midas and Croesus. He discusses why gold is unique in its malleability and ductility, far greater than any other metal. The examples given are its