[De epidemia et peste]

who are in a place where good air is accustomed to be, at the time when there is no epidemic, such people receive bad impressions more quickly and die more quickly at the time of an epidemic. Whence Avicenna, chapter on good air: "When a common, open putrefaction occurs in the air, then it will be more receptive to it than that which is constricted and hidden; however, the open is better." Whence, sometimes with an epidemic, measles come, sometimes smallpox, sometimes ophthalmia, and other things of this kind.

Chapter Three: On preservation from an epidemic through the correction of the air and through departure from the place in which it is present.

It is much easier to assist in preserving, and indeed one is more secure, than in curing after they are actually sick. Therefore, let us speak about preservation. Preservation from pestilence is to flee, not only the place but also the whole land, as Rasis says, and the further away, the more secure, because he who is not in the corrupt and putrefied air is not corrupted by it, just as he who is not in battle does not die in it. If, however, it is necessary to remain in a place where such pestilence is present, then the first aid is taken from the air of the house in which one remains. For the house must be clean from any waste whatsoever, especially that which generates a stench, far from dunghills and from stagnant waters, and the orifices of latrines should be closed. When the air is misty or foggy, one should not rise in the morning. Also, when the south or subsolan wind blows, then fumigations, which will be discussed below, should be made. And when one rises, smell vinegar and rose water, because smelling this is valid in hot and cold weather because it restricts and strengthens.