[84] for the man who is improved by instruction, having received a happy and virtuous nature, uses that virtue alone which, by means of memory co-operating with it, implants in him an absence of forgetfulness, so that he comprehends and takes firm hold of all the things which he has once learnt; but he who practises virtue, since he is continually exercising himself, stops to take breath, and relaxes his efforts for a while, collecting himself and recovering the vigour which was a little impaired by his exertions, just as those men do who have oiled their bodies for the contests in the arena. For these men, also, labouring at their training exercises, in order to prevent their powers being utterly broken down, anoint themselves with oil on account of the violent and continued nature of their exercise.