(Ἡρόδικος), a physician of Selybria or Selymbria in Thrace, who lived in the fifth century B. C. He was one of the tutors of Hippocrates (Suid. s. v. Ἱπποκράτης; Sorani Vita Hiippocr.; Jo. Tzetz. Chil. vii. Hist. 155. ap. Fabric. Bibl. Graec. vol. xii. p. 681, ed. vet.). He is mentioned, together with Iccus of Tarentum, as being one of the first persons who applied gymnastics to the treatment of disease and the preservation of health. (Plat. Protag. § 20. p. 316; Lucian, Quomiodo Histor. sit conscrib. § 35.) He was not only a physician, but also a παιδοτρίβης, or gymnastic-master (Plat. De Rep. iii. p. 406), and a sophist (Id. Protag. l. c.), and was induced to study gymnastics in a medical point of view, from having himself been benefited by them. From a passage in Plato (Phaedr. init., et Schol.), it has been supposed that he used to order his patients to walk from Athens to Megara, and to return as soon as they had reached the walls of the latter town. The distance, however, which would be more than seventy miles, renders this quite impossible ; nor do the words of Plato necessarily imply that he ever gave any such directions. A passage also in the sixth book of Hippocrates, De Morbis Vulgaribus (6.3, vol. iii. p. 599), has been quoted as confirming Plato's words, and accusing Herodicus of killing his patients by walking, &c. ; but the reading in this place is uncertain, and M. Littré considers that we should probably read Πρόδικος, and not Ἡρόδικος (Oeuvres d'Hippocr. vol. i. p. 51). It should, however. be added, that Galen, in his commentary on the above passage (3.31, vol. xvii. pt. ii. p. 99), though he reads Πρόδικος, considers him to be the same person who is mentioned by Plato; and Pliny, when he speaks of Prodicus (H. N. 29.2), is probably alluding to him also. He is mentioned by several other ancient authors; as Plutarch (De Sera Num. Vind. 100.9.), Aristotle (De Rhet. 1.5.10), Eustathius (ad Il. i. p. 763, 16), Caelius Aurelianus (De Morb. Chron. 5.1), and in Cramer's Anecd. Graec. Paris. vol. iii.