[34] Thucydides mentions that the mortality of the plague was greatly aggravated by the influx of the people from the country into the city, and the crowding of them in ill-ventilated huts. (ii., 52.) Mitford, in describing the plague of Athens, remarks that the want of sewers in ancient times must have contributed very much to the severity of the disease. (Hist. of Greece, vol. ii., p. 195.) He refers (l. c.) to Strabo (Geogr. v.) for proof that the Romans were the first people who constructed sewers.
[35] See Xenophon, Cyropæd., i. and viii.
[36] Galen, Comment in libr. de Artic. iii.
[37] Xenophon, Anabasis, i. It has never been clearly determined whether he was in the suite of Artaxerxes the king, or of his brother Cyrus, before the battle of Cunaxa, in which the latter was killed, and the former being severely wounded, was attended professionally by Ctesias. Diodorus Siculus, indeed, says decidedly that he was taken prisoner on the occasion. (Bibl. ii., 32.) But we are certain, from the authentic narrative of Xenophon, that he was not taken prisoner in the battle, nor is it likely that he was one of those who were kidnapped afterwards, otherwise the historian would certainly not have omitted the name of so distinguished a personage. Besides, had he been brought to Babylon in this way, as a captive, Artaxerxes was not likely to have intrusted his royal life to a person who had been so lately the professional attendant on his rebel brother.
[38] See Thucyd., ii., 48.
[39] De Prisca Medicina.
[40] See in the next section, under xxiii. Though I have not admitted the treatise here referred to into the list of genuine works, it will be seen below that it possesses considerable evidence in its favor, and that beyond doubt it is very ancient.
[41] Aphor., I., 1.
[42] See Galen, Opera, tom. v., p. 488; ed. Basil.
[43] This is clearly defined and stated by Aristotle, Phys., i. See also Boethius in Præd., p. 113; ed. Basil.