You are sick, that's sure

"You are sick, that's sure," — they say: "Sick of what?" — they disagree. " 'T is the brain," — thinks Doctor A; " 'T is the heart," — holds Doctor B; "The liver — my life I'd lay!" "The lungs!" "The lights!" Ah me! So ignorant of man's whole Of bodily organs plain to see — So sage and certain, frank and free, About what's under lock and key — Man's soul!