After his early success in the national market, Fitzgerald began writing his Great Brain books. He later recalled that he had never thought of writing a book for children until one evening when friends dropped in and began to reminisce about their childhoods. They laughed so much his wife suggested he write a book about Tom. Dell Publishers brought out The Great Brain in 1969, followed by six more volumes of boyhood adventures featuring this keen-witted Fitzgerald. These books resemble a chat around the fireside.
Conversations flow easily as story after story is told, each one getting more outlandish.
In one of these tales, John is trying to get the mumps before his brothers. In the past, whenever one boy became ill Mamma put the other children to bed with him so they could all get it and have it over with. The story describes John's efforts to catch the disease from a friend by creeping into his room in great secrecy and asking him to breathe on him. He describes his satisfaction that when he is almost over the mumps, Tom and Sweyn will just be getting sick. Every morning he checks the mirror to see if signs of the illness are apparent yet.