What are some characteristics of Mr. Nuttel?

In addition to the obvious facts that Framton Nuttel is a neurotic suffering from what in those days was called a "nervous disorder," the author indicates that Nuttel is shy, introverted, and timid. His sister has to force letters of introduction on him, so that he will feel obliged to get around and meet some people in the rural setting where he has gone for his "nerve cure." 

Privately he doubted more than ever whether...

In addition to the obvious facts that Framton Nuttel is a neurotic suffering from what in those days was called a "nervous disorder," the author indicates that Nuttel is shy, introverted, and timid. His sister has to force letters of introduction on him, so that he will feel obliged to get around and meet some people in the rural setting where he has gone for his "nerve cure." 

Privately he doubted more than ever whether these formal visits on a succession of total strangers would do much towards helping the nerve cure which he was supposed to be undergoing.

His sister, who has known him all his life, gives some worthwhile information about Framton's character.

     "I know how it will be," his sister had said when he was preparing to migrate to this rural retreat; "you will bury yourself down there and not speak to a living soul, and your nerves will be worse than ever from moping."

In modern times he would not have been sent to the country but would have been referred to a psychotherapist, and he could have spent many years talking to a father figure about his symptoms. This is what he seems to be looking for. He tells Mrs. Sappleton all about his doctors and their diagnoses when he first meets her. She will later describe him to her husband as follows:

"A most extraordinary man, a Mr. Nuttel," said Mrs. Sappleton; "could only talk about his illnesses, and dashed off without a word of goodby or apology when you arrived. One would think he had seen a ghost."

The reader may wonder whether Framton's experience at the Sappletons' country home will be helpful or harmful. The three "ghosts" may have made him more nervous than ever before. But on the other hand, his successful escape and his vigorous exercise may have bolstered his morale. No doubt he will find out eventually that he was the victim of a practical joke, and this may have the curative effect of prompting him to laugh at himself.

Framton's symptoms are mainly imaginary, which indicates that he has a vivid imagination. In this respect he is like young Vera. Maybe she understands him intuitively after only talking to him for a few minutes. She might even understand that he is like herself in being bored with life and looking for a little excitement. His introversion, shyness, and timidity have inclined him to spend much of his time alone. This is not good for people. His "nervous disorder" may be largely due to his introversion and seclusion.