In "Three Men in a Boat," why did the writer go to the British Museum? What did he discover when he went through the medical book alphabetically?

This reference appears in the opening pages of the book. The narrator and his friends are sharing information about the ailments they each suffer from. This exchange reminds the narrator of a time when he went to the British Museum to discover a treatment for hay fever. He searched through a medical book for the answer, and then began to turn pages at random to read up on other ailments. To his horror he found that he had the symptoms of each and every disease or malady that was listed in the book. He then went through the listings alphabetically, from ague to zymosis, to make sure he was right. The only entry he didn’t find anything in common with was “housemaid’s knee.” Presumably a person would get such a pain by scrubbing a floor by hand – something which this gentlemen would never do. Savvy readers will realize that the narrator is either exaggerating about this episode, or he has a tendency toward reacting disproportionately and experiencing psychosomatic illnesses, or all of the above.