I wasn’t sure I would be able to find a topic relevant to the Panama-Pacific International Exposition for the letter X. Turned out my instincts was correct. So far, I’d been unable to find anything listed in the indices of my favorite books.
Growing up in Ireland, my mom always gave me a couple of Ladybird book at Christmas and on my birthday. These thin books were a sort of precursor to the Dorling Kindersley (DK) Books in topic though focused on a single story and without all the callouts and extensive photography. Both series are wonderful for children.
I tried a few searches for the topic of X-rays and the PPIE, and was surprised to learn something new: the Panama-Pacific International Exposition had a working X-ray machine in its hospital and several manufacturers were at the expo selling similar machines for use in clinical settings.