But presently the Doctor noticed that after they had licked the gum off the stamps, the customers would bring them back and want to exchange them for money again. Now, it is a rule that all post offices have to exchange their own stamps, when asked, for the price paid for them. So long as they are not torn or marked it doesn't matter whether the gum has been licked off or not. So the Doctor saw that he would have to change his kind of gum if he wanted to keep stamps that would stick.
And one day the King's brother came to the post office with a terrible cough and asked him in the same breath (or gasp) to give him five half-penny stamps and a cure for a cough. This gave the Doctor an idea. And the next gum which he invented for his stamps he called whooping-cough gum. He made it out of a special kind of sweet, sticky cough-mixture. He also invented a bronchitis gum, a mumps gum and several others. And whenever there was a catching disease in the town the Doctor would see that the proper kind of gum to cure it was issued on the stamps. It saved him a lot of trouble, because the people were always bothering him to cure colds and sore throats and things. And he was the first Postmaster General to use this way of getting rid of sickness—by serving round pleasant medicine on the backs of stamps. He called it stamping out an epidemic.
One evening at six o'clock Jip shut the doors of the post office as usual, and hung up the sign "Closed" as he always did at that hour. The Doctor heard the bolts being shot and he stopped counting postcards and took out his pipe to have a smoke.
"Jip hung up the sign"
The first hard work of getting the post office in full swing was now over. And that night John Dolittle felt when he heard the doors being shut that at last he could afford to keep more regular hours and not be working all the time. And when Jip came inside the Registered Mail booth he found the Doctor leaning back in a chair with his feet on the desk, gazing around him with great satisfaction.
"Well, Jip," said he with a sigh, "we now have a real working post office."