MH page 262

The noise and excitement and confusion of the cities, their constrained and artificial life, are most wearisome and exhausting to the sick. The air, laden with smoke and dust, with poisonous gases, and with germs of disease, is a peril to life. The sick, for the most part shut within four walls, come almost to feel as if they were prisoners in their rooms. They look out on houses and pavements and hurrying crowds, with perhaps not even a glimpse of blue sky or sunshine, of grass or flower or tree. Shut up in this way, they brood over their suffering and sorrow, and become a prey to their own sad thoughts.

City environments containing pollution, confinement, and confinement-related rumination are detrimental to the sick. It details specific environmental exposures in cities and their psychological and physical impacts on patients.