The common effect of all kinds of exercise is to produce an increase of the natural heat of animals. But each species has something peculiar to it. Strong, that is to say, violent exercise gives vigour to the muscles and nerves: such are digging, and lifting a very heavy burden, while one remains in the same spot, or moves about; or lifting small weights and walking about as much as one can. Of this kind, is the exercise of scaling a rope, and many others of a like kind. The swift kinds of exercise are such as do not require strength and violence, namely, running, fighting with one’s shadow, wrestling with the extremities of the hands, the exercise with the leather bag, and that with the small Ball. This last is compounded of intension and velocity; and such exercises as are intense may become violent by adding velocity to them. Besides, some kinds of exercise bring the loins into action, and some the hands or legs; others the spine or the chest alone, or the lungs. And exercise ought to be carried on until the body becomes distended, and the skin of a florid hue; and until then, the motions ought to be strong, equable, and spirited, upon which you may see warm sweat, mixed with vapour, break out. It will then be time for you to stop, when any of the symptoms which I have mentioned have undergone a change, namely, when the bulk of the body becomes contracted, or when the florid colour of the skin declines. And, should any of the motions remit, it will then be time to stop immediately; or, if there should be any change in the quantity or quality of the perspiration; for if it should become smaller in quantity, or colder, we must desist, and, besmearing the body with oil, endeavour to restore it. It will then be proper to use the Restorative friction, as the masters of gymnastics are wont to practise. * * * * * COMMENTARY. We shall now give a brief account of the ancient exercises, some of which are altogether omitted by our author. The σκιομαχία is thus explained by Cornarius: “Porro σκιομαχίαν accipio umbratilem pugnam, quâ quis privatim domi aut sub umbra, non in propatulo se exercet, ac veluti præparat ad justam pugnam publicè faciendam.” (Notæ in Paul. Ægin. h. 1.) This account, however, does not agree with that of Oribasius, who describes it as a mock encounter at boxing and jumping with one’s own shadow. (Med. Collect. vi, 29.) It is thus described in the Latin translation of Avicenna: “Et ex eis est, insequi umbram suam, ut ipsam percutiat in capite, et manus ad invicem percutere.” (i, 3, 2, 2.) It is mentioned in this sense by Plato (de Legibus, vii), by Plutarch (Probl. Conviv. vii), and by Achilles Tatius (p. 115.) Juvenal probably alludes to this sport. (Sat. vi, 246.) We have therefore translated it, “fighting with one’s own shadow.”