Of ἀιώρα, or _gestation_, there were various modes. That in a carriage was very ancient, and is often mentioned by the medical authors. It appears from Pliny (Hist. Nat. xvi, 42), that carriages were generally made of fir, and that the axles were of ilex, mountain ash, or elm. Sometimes, however, the whole chariot was adorned with gold and silver. (Pliny, Hist. Nat. xxiv, 17.) They appear to have been often covered in with skins. (Plutarch, Prob. Roman.) They were generally drawn by horses or mules, sometimes by oxen, and occasionally by slaves. They were so constructed that a person could either sit or lie, according to pleasure. (Galen, Hyg.) At first, according to Pliny, they had only two wheels; the Phrygians, he says, added two more; and Hippocrates mentions that the Scythians introduced the use of six-wheeled carriages. The sedan and chair are often mentioned by the Latin poets, as well as by the medical writers. It is sufficient for our purpose to state that they were so constructed, that one could either sit or lie in them. They sometimes had windows, formed from the lapis specularis. (Juvenal, Sat. iv, 21.) Navigation, or sailing in ships and boats, is often mentioned by ancient authors as a remedial measure. It was practised on the sea or in rivers. According to Aëtius, gestation in general ventilates the natural heat, produces excitement, dispels collected humours, strengthens the frame, and rouses the actions when in an indolent state. (iii, 6.) Celsus has an interesting chapter on gestation. The following rule for the application of it is very judicious: “Gestatio quoque longis et jam inclinatis morbis aptissima est; utilisque est et iis corporibus quæ jam ex toto febre carent, sed adhuc exerceri per se non possunt; et iis quibus lentæ morborum reliquiæ remanent, neque aliter eliduntur.” Upon the whole, he holds it to be a doubtful practice in ardent fever, although sanctioned by the authority of Asclepiades Bithynus: at all events, he insists that gestation is improper when there is any local pain or swelling. After characterizing the different modes of gestation, he remarks respecting them: “Levia quidem genera exercitationis infirmis conveniunt: valentiora vero iis qui jam pluribus diebus febre liberati sunt; aut iis, qui gravium morborum initia sic sentiunt, ut adhuc febre vacent, quod et in tabe, et in stomachi vitiis, et cum aqua cutem subiit, et interdum in regio morbo fit; aut ubi quidam morbi, qualis comitialis, qualis insania est, sine febre, quamvis diu, manent.” (ii, 15.)