About good air

Air that is good in substance is air in which there is no foreign admixture of steam or smoke. It should be open to the sky and not enclosed in walls or under a roof, of course, except in cases where the air has undergone general deterioration, then open air is more susceptible to it than closed and enclosed air. And in other cases, open air is better. This good air is clean and transparent: it is not mixed with evaporation from lowlands, thickets, ditches, wetlands and vegetable gardens, especially those where, for example, cabbage and indau are sown, as well as evaporation from those places where trees and bad trees grow densely by substance, such as nuts, shauhat, figs, and putrefactive winds blow. However, it should not be closed to good winds, since they blow from elevated and level places. Such air is not confined to the lowlands, which quickly heats up after sunrise and quickly | cools down after sunset, and is not locked into walls that have recently been covered with lime plaster or something of the like and are not yet completely dry, and also does not resist breathing, as if grabbing a person by the throat.

You already know that changes in the air are natural, but there are also unnatural ones, and there are also those that, while not being natural, at the same time do not go beyond the limits of the natural.

Know that changes in the air that do not come from nature are sometimes opposite to nature, and sometimes they are not.

Some of them occur periodically, others do not maintain periodicity. The circumstances of the seasons are healthiest when they correspond to their nature, and changing the nature brings on illness.