This reference appears in the opening pages of Three Men in a Boat. The narrator tells us about a time when he went to the British Museum to discover a treatment for hay fever. He picked up a medical book to find the answer, and then began to read up on other ailments. To his horror, he discovered that he had the symptoms of almost every disease or malady that was listed. At first he thought this status would make him a perfect example for medical study, since he suffered from everything.
“What an acquisition I should be to a class! Students would have no need to ‘walk the hospitals,’ if they had me. I was a hospital in myself.”
Then he began to worry about himself and his real health. This story shows us early on that the narrator tends to exaggerate, to react disproportionately to situations, and to become distracted by side stories and tangents. Did he really suffer from all of these diseases? No. Therefore, we need not agree with his projected metaphor about being a hospital in himself. But he gives us an interesting literary analogy to consider.