[144] Therefore in the same manner, if all the elements of the world together were all to disappear at one and the same moment, then it would be necessary to admit that the world was liable to corruption and destruction; but if each of these elements separately only changes its nature so as to assimilate to that of its nature, it is then rendered immortal rather than destroyed, according to the philosophical statement of the tragic "Nought that has once existed dies, Though often what has been combined Before, we separated find, Invested with another form."