This is the first story told by narrator J. in Three Men in a Boat. Here he sets the stage for the rest of the book in two ways. First, he allows us to quickly become familiar with his humorous style of storytelling, which he will employ throughout the narrative. Secondly, he reveals just one of his own personality quirks, which foreshadows the appearance of many more to come.
When he consulted the medical book at the British Museum, J. proceeded through it alphabetically, from “ague” to “zymosis.” He was such a hypochondriac that he thought he had some symptoms of every disease listed, except for “housemaid’s knee.” Here’s an example of his sense of humor. Yes, such a disease with this name exists. Its medical term is Prepatellar bursitis, which is an inflammation of the kneecap. But it’s common only in people who spend a lot of time kneeling—like old-fashioned servants who must mop up floors by hand. J. is a gentleman of some sort. We don’t know what kind of employment he may have, or even if he has any employment at all. But he’s certainly not the kind of gentleman who would have to clean his own floors on his hands and knees. He would have no need to kneel, ever. Already, we can understand how he views himself in the British society life of the late 19th century.