Counsel Against the Plague

to the vital spirit: I say hostile not because of elemental quality, but because of specific property, just as theriac is. It is not exactly a friend because it is hot, or cold, or dry, or moist, but because its entire composition results in a form proportionate to the form of the vital spirit. Thus, that pestilential vapor is not hostile exactly because of heat, cold, dryness, or moisture, but because its proportion is almost exactly contrary to the proportion in which the vital spirit of the heart consists. And just as poisons are born continually in the earth, so too does this poisonous vapor sometimes arise in the air. But it is not so potent, because it is more diffused. It cannot become fixed in pure air, because such air is conformable to the spirit: and just as fire, because by its power it does not take on mixture—that is, a mingling with another nature—therefore it does not putrefy, so pure air, not having mixture, has no putrefaction. Likewise, the said poisonous vapor does not attach itself to the human body unless there are humors apt for fever, which are humors disposed to putrefy and to catch fire. If the vital spirit is weaker than it, the spirit flees from it as from its contrary. If it is more potent, it removes it from itself. Therefore, it is necessary to correct the air, to purge Theriac