They have sought it since the first alchemist put an elixir of life on the same shopping list as a way to turn lead into gold.
In particular they sought a fanciful substance called "the elixir of life", a powerful medicine which was to cure all illness, and which some people thought would turn out to be the same substance as "the philosopher's stone".
According to the myth of the moon, Chang E drank the elixir of life and Wu Kang cut down the cassia tree which can restore itself with each blow, implying an immortal spirit of life.
The search for an elixir of life has taken people to some strange places. Few, though, are stranger than rotifers.
Earlier this year fish oil was hailed as the 'elixir of life' after scientists from the University of California, San Francisco found it could have a direct effect on extending the lifespan of cells.
Chang-Er flew to the moon with the elixir of life,chased by her famous archer-husband
