Final answer:
Weir Mitchell was a prominent physician who specialized in neurology and mental illness. John threatens to send the narrator to him as a form of punishment.
Step-by-step explanation:
Weir Mitchell was a widely known and influential physician in the late 19th and early 20th centuries. He was a specialist in neurology and mental illness, and his methods included the use of rest cures and isolation. In the context of the question, John threatens to send the narrator to Weir Mitchell, meaning that he would be sending the narrator to a facility where Dr. Mitchell's methods are practiced.