Zeno (7) (2nd cent. bce), a physician of the ‘school’ of *Herophilus, participated in the Herophilean traditions of innovative pulse theory, *pharmacology, and Hippocratic lexicography (see hippocrates(2)). He achieved more lasting prominence, however, by ‘decoding’ (and attributing to Hippocrates himself) certain letter symbols (χαρακτῆρες), such as Δ̨ΕΗΘ or ΞΖΘ, found in clusters of four or five at the conclusion of individual case histories in some *Alexandrian manuscripts of the Hippocratic work Epidemics 3. Members of the Empiricist school of medicine (see medicine, § 5.3), including *Heraclides (4) of Tarentum, fiercely attacked Zeno's views about the provenance and meaning of the symbols. Some Empiricists, attributing the invention of the symbols to Mnemon of Side, charged Zeno with altering the marks whenever he could not find a plausible interpretation; another Empiricist, Apollonius Byblas, questioned the authenticity of the symbols, claiming that Zeno's version of the symbols in Epidemics 3, case-history 8, could not be found in any of three copies of the Hippocratic treatise that he had examined.