What does James need to do to the little green crocodile tongues to get them working?

At the beginning of the story, James is approached by a peculiar old man with a small paper bag. Inside the paper bag, there are "a mass of tiny green things" that the old man tells him are crocodile tongues. The old man gives the bag to James and tells him how to use the tongues to make a potion that will magically make "marvelous . . . fabulous, unbelievable things" happen to James. The old man promises James that if he follows his instructions, he will "never be miserable again."
To make the potion correctly, James is told that he must first of all pour all of the crocodile tongues into "a large jug of water." Next he must slowly add ten single hairs, one by one, from his own head. The hairs, the old man says, will set the crocodile tongues off and "get them going." After that, when the mixture starts to "froth and bubble furiously," the old man says that James must drink the potion, "the whole jugful, in one gulp." James is warned that he will then start to feel the potion "churning and boiling" in his stomach and that steam will start coming out of his mouth. "Immediately after that," the old man, says, the crocodile tongues will have worked their magic, and the aforementioned "marvelous . . . fabulous, unbelievable things" will start to happen.