I have two doctors, my left leg and my right.

Trevelyan’s quip treats walking (or regular physical exercise) as a kind of medicine: the “two doctors” are simply the legs that carry one into daily movement. The line belongs to a long tradition of health maxims—especially among writers and public intellectuals—praising exercise as preventive care and as a remedy for melancholy, sluggishness, and the ailments of sedentary life. Its humor lies in reducing medical authority to something everyone already possesses, implying self-reliance and the idea that many complaints are better met with habitual activity than with pills or consultations. Read broadly, it also gestures toward balance and moderation: steady, ordinary motion as a sustaining discipline.