One of Mary Poppins’ most famous songs began with a child’s trip to the school nurse.

In the early 1960s, songwriter Robert B. Sherman was working with his brother Richard on the music for Walt Disney’s Mary Poppins. They needed a new song. An earlier number had not worked, and Walt Disney had asked them to come up with something better suited to Mary Poppins and her approach to getting unpleasant jobs done.

Then Robert’s young son Jeffrey came home from school and mentioned that he had received the polio vaccine.

Robert knew his son disliked needles and asked whether the vaccination had hurt. Jeffrey explained that there had been no injection. The vaccine had been placed on a sugar cube, which he simply ate.

Robert immediately recognized the makings of a song. He called his brother, and the idea became “A Spoonful of Sugar,” one of the best-known numbers in the 1964 film.

The medicine was Albert Sabin’s oral polio vaccine. Unlike Jonas Salk’s earlier injected vaccine, Sabin’s vaccine could be swallowed. Because it had a bitter, salty taste, it was sometimes administered to children on a sugar cube or with sweet syrup. Its ease of administration helped it become widely used during the massive effort to control polio.