Again, not merely by way of pleasures, but by way of pains also, the body operates to entail evil or wickedness on the soul. When acid or salt phlegm--when bitter and bilious humours--come to spread through the body, remaining pent up therein, without being able to escape by exhalation,--the effluvia which ought to have been exhaled from them become confounded with the rotation of the soul, producing in it all manner of distempers. These effluvia attack all the three different seats of the soul, occasioning great diversity of mischiefs according to the part attacked--irascibility, despondency, rashness, cowardice, forgetfulness, stupidity. Such bad constitution of the body serves as the foundation of ulterior mischief. And when there supervene, in addition, bad systems of government and bad social maxims, without any means of correction furnished to youth through good social instruction--it is from these two combined causes, both of them against our own will, that all of us who are wicked become wicked. Parents and teachers are more in fault than children and pupils. We must do our best to arrange the bringing up, the habits, and the instruction, so as to eschew evil and attain good.[105] [Footnote 105: Plato, Timæus, p. 87 A-C.] [Side-note: Preservative and healing agencies against disease--well-regulated exercise, of mind and body proportionally.] After thus describing the causes of corruption, both in body and mind, Plato adverts to the preservative and corrective agencies applicable to them. Between the one and the other, constant proportion and symmetry must be imperatively maintained. When the one is strong, and the other weak, nothing but mischief can ensue.[106] Mind must not be exercised alone, to the exclusion of body; nor body alone, without mind. Each must be exercised, so as to maintain adequate reaction and equilibrium against the other.[107] We ought never to let the body be at rest: we must keep up within it a perpetual succession of moderate shocks, so that it may make suitable resistance against foreign causes of movement, internal and external.[108] The best of all movements is, that which is both in itself and made by itself: analogous to the self-continuing rotation both of the Kosmos and of the rational soul in our cranium.[109] Movement in itself, but by an external agent, is less good. The worst of all is, movement neither in itself nor by itself. Among these three sorts of movement, the first is, Gymnastic: the second, propulsion backwards and forwards in a swing, gestation in a carriage: the third is, purgation or medicinal disturbance.[110] This last is never to be employed, except in extreme emergencies. [Footnote 106: Plat. Tim. pp. 87-88 A.] [Footnote 107: Plat. Tim. p. 88 C.] [Footnote 108: Plat. Tim. p. 88 D-E.]