that great medicine

Alluding, perhaps, to the philosopher’s stone, which, by its touch, was said to convert base metal into gold. The alchemists called the matter, whatever it was, by which they performed transmutation a medicine. So Chapman in his Shadow of Night, 1594: O then, thou great elixir of all treasures. And on this passage he has the following note: The philosopher’s stone, or philosophica medicina, is called the great elixir. Walker thinks that medicine here means physician, and so the word was sometimes used.