Third of the Sector General books. A group of novelettes telling the story of the hospital ship's meeting with creatures from the planet that the Cultural Contact and Survey crew had dubbed "Meatball". Sector General had met many a challenge that was literally out of this world, but these entities were a really special case.
Recommend reading "Sector General" first to get an overview of James White's "hospital in space" world. Imagine a hospital where many different species from all over the galaxy work together to teach, operate and solve medical problems. Imagine one of those species inside your head to help you operate on a third species... imagine carrying many of them inside your head... James White's series is highly addictive, and follow the same thread through each book. He does explain his layout of the variety of species in each book, but
"Sector General" will set you up for the others.