back to The Dragon
The hydra is another form of the dragon with the same symbolic meaning.
Here we see Hercules, with lion skin and club, attack the hydra of Lerna, one of his Twelve Works (in alchemy there also twelve operations). In the Greek story, each time one of the seven heads of the hydra was cut of, it would sprout a new one. In the story this problem was solved by his friend who burnt the necks shut with fire.
In this image, Hercules friend is Mercury, who is the Matter of the Great Work, that is the mind of the alchemist.
The story of the hydra of Lerna is about the elimination of thoughts during meditation. The thought process is so persistent that each time a thought is removed another pops up immediately.
Mercury is pouring water on the hydra. Watering the Matter, and one has to water it again and again, is a term used to indicate the ongoing purification of the Matter.