Plato next explains the construction of ligaments and flesh--of the mouth, tongue, teeth, and lips: of hair and nails.[95] These last were produced with a long-sighted providence: for the Gods foresaw that the lower animals would be produced from the degeneration of man, and that to them nails and claws would be absolutely indispensable: accordingly, a sketch or rudiment of nails was introduced into the earliest organisation of man.[96] Nutrition being indispensable to man, the Gods produced for this purpose plants (trees, shrubs, herbs, &c.)--with a nature cognate to that of man, but having only the lowest of the three human souls.[97] They then cut ducts and veins throughout the human body, in directions appropriate for distributing the nutriment everywhere. They provided proper structures (here curiously described) for digestion, inspiration, and expiration.[98] The constituent triangles within the body, when young and fresh, overpower the triangles, older and weaker, contained in the nutritive matters swallowed, and then appropriate part of them to the support and growth of the body: in old age, the triangles within are themselves overpowered, and the body decays. When the fastenings, whereby the triangles in the spinal marrow have been fitted together, are worn out and give way, they let go the fastenings of the soul also. The soul, when thus released in a natural way, flies away with delight. Death in this manner is pleasurable: though it is distressing, when brought on violently, by disease or wounds.[99] [Footnote 95: Plato, Tim. pp. 75-76.] [Footnote 96: Plat. Tim. p. 76 E. [Greek: o(/then e)n a)nthrô/pois eu)thu\s gignome/nois _u(petupô/santo_ tê\n tô=n o)nu/chôn ge/nesin.]] [Footnote 97: Plat. Tim. p. 77 B-C.] [Footnote 98: Plat. Tim. pp. 78-79.] [Footnote 99: Plat. Tim. p. 81.] [Side-note: General view of Diseases and their Causes.] Here Plato passes into a general survey of diseases and the proper treatment of them. "As to the source from whence diseases arise (he says) this is a matter evident to every one. They arise from unnatural excess, deficiency, or displacement, of some one or more of the four elements (fire, air, water, earth) which go to compose the body."[100] If the element in excess be fire, heat and continuous fever are produced: if air, the fever comes on alternate days: if water (a duller element), it is a tertian fever: if earth, it is a quartan--since earth is the dullest and most sluggish of the four.[101] [Footnote 100: Plat. Tim. p. 81 E. [Greek: to\ de\ tô=n no/sôn o(/then xuni/statai, dê=lo/n pou kai\ panti/.]] [Footnote 101: Plat. Tim. p. 86 A. [Greek: to\ de\ gê=s, teta/rtôs o)\n nôthe/staton tou/tôn.]] [Side-note: Diseases of mind--wickedness is a disease--no man is voluntarily wicked.]