This is the most authoritative contemporary statement of the nature of the plague . . . The full text consists of two parts: three chapters on the causes of the plague, and seven on remedies and regimen. Only the first part is printed here.

[Source: R. Hoeniger, ed., Der Schwarze Tod (Berlin, 1882), appendix III, pp. 152-6.]

We shall divide the work into two parts, in the first of which we shall investigate the causes of this pestilence and whence they come, for without knowledge of the causes no one can prescribe cures. In the second part we shall include methods of prevention and cure. There will be three chapters in the first part, for this epidemic arises from a able cause. One cause is distant and from above, and pertains to the heavens; the other is near and from below and pertains to the earth, and is dependent, causally and effectively, on the first cause. Therefore first chapter will deal with the first cause, the second with the second cause, and the third with the prognostications and signs associated with both of them. There will be two treatises in the second part. The first will deal with medical means of prevention and cure and will be divided into four chapters: the first on the disposition of the air its rectification; the second on exercise and baths; the third on food and drink; the fourth on sleeping and waking, emptiness and fullness the stomach and on the emotions. The second treatise will have three chapters: the first on universal remedies; the second on specific remedies appropriate to different patients; the third on antidotes.

CHAPTER 1 OF THE FIRST PART: CONCERNING THE UNIVERSAL AND DISTANT CAUSE

We say that the distant and first cause of this pestilence was and is the configuration of the heavens. In 1345, at one hour after noon on 20 March, there was a major conjunction of three planets in Aquarius. This conjunction, along with other earlier conjunctions and eclipses, by causing a deadly corruption of the air around us, signifies mortality and famine - and also other things about which we will not speak here because they are not relevant. Aristotle testifies that this is the case in his book Concerning the causes of the properties of the elements,[n. 2] in which he says that mortality of races and the depopulation of kingdoms occur at the conjunction of Saturn and Jupiter, for great events then arise, their nature depending on the trigon in which the conjunction occurs. And this is found in ancient philosophers, and Albertus Magnus in his book, Concerning the causes of the properties of the elements (treatise 2, chapter 1) says that the conjunction of Mars and Jupiter causes a great pestilence in the air, especially when they come together in a hot, wet sign, as was the case in 1345.[n. 3]  For Jupiter, being wet and hot, draws up evil vapours from the earth and Mars, because it is immoderately hot and dry, then ignites the vapours, and as a result there were lightnings, sparks, noxious vapours and fires throughout the air.

CHAPTER 2 OF THE FIRST PART: CONCERNING THE PARTICULAR AND NEAR CAUSE

Although major pestilential illnesses can be caused by the corruption of water or food, as happens at times of famine and infertility, yet we still regard illnesses proceeding from the corruption of the air as much more dangerous. This is because bad air is more noxious than food or drink in that it can penetrate quickly to the heart and lungs to do its damage. We believe that the present epidemic or plague has arisen from corrupt air in its substance, and has not changed in its attributes.[n. 7]  By which we wish it be understood that air, being pure and clear by nature, can only become putrid or corrupt by being mixed with something else, that is to say, with evil vapours. What happened was that the many vapours which had been corrupted at the time of the conjunction were drawn up from the earth and water, and were then mixed with the air and spread abroad by frequent gusts of wind in the wild southerly, gales, and because of these alien vapours which they carried the winds corrupted the air in its substance, and are still doing so. And this corrupted air, when breathed in, necessarily penetrates to the heart and corrupts the substance of the spirit there and rots the surrounding moisture, and the heat thus caused destroys the life force, and this is the immediate cause of the present epidemic.[n. 8] 

And moreover these winds, which have become so common here, have carried among us (and may perhaps continue to do so in future) bad, rotten and poisonous vapours from elsewhere: from swamps, lakes and chasms, for instance, and also (which is even more dangerous) from unburied or unburnt corpses - which might well have been a cause of the epidemic. Another possible cause of corruption, which needs to be borne in mind, is the escape of the rottenness trapped in the centre of the earth as a result of earthquakes - something which has indeed recently occurred. But the conjunctions could have been the universal and distant cause of all these harmful things, by which air and water have been corrupted.

CHAPTER 3: CONCERNING PROGNOSTICATION AND SIGNS 

Unseasonable weather is a particular cause of illness. For the ancients, notably Hippocrates, are agreed that if the four seasons run awry, and do not keep their proper course, then plagues and mortal passions are engendered that year. Experience tells us that for some time the seasons have not succeeded each other in the proper way. Last winter was not as cold as it should have been, with a great deal of rain; the spring windy and latterly wet. Summer was late, not as hot as it should have been, and extremely wet - the weather very changeable from day to day, and hour to hour; the air often troubled, and then still again, looking as if it was going to rain but then not doing so. Autumn too was very rainy and misty. It is because the whole year here - or most of it - was warm and wet that the air is pestilential. For it is a sign of pestilence for the air to be warm and wet at unseasonable times.

We have not said that the future pestilence will be exceptionally dangerous, for we do not wish to give the impression that it will be as dangerous here as in southern or eastern regions. For the conjunctions and the other causes discussed above had a more immediate impact on those regions than on ours. However, in the judgement of astrologers (who follow Ptolemy on this) plagues are likely, although not inevitable, because so many exhalations and inflammations have been observed, such as a comet and shooting stars.[n. 10]  Also the sky has looked yellow and the air reddish because of the burnt vapours. There has also been much lightning and flashes and frequent thunder, and winds of such violence and strength that they have carried dust storms from the south. These things, and in particular the powerful earthquakes, have done universal harm and left a trail of corruption. There have been masses of dead fish, animals and other things along the sea shore, and in many places trees covered in dust, and some people claim to have seen a multitude of frogs and reptiles generated from the corrupt matter; and all these things seem to have come from the great corruption of the air and earth. All these things have been noted before as signs of plague by numerous wise men who are still remembered with respect and who experienced them themselves.

The bodies most likely to take the stamp of this pestilence are those which are hot and moist, for they are the most susceptible to putrefac­tion. The following are also more at risk: bodies bunged up with evil hu­mours, because the unconsumed waste matter is not being expelled as it should; those following a bad life style, with too much exercise, sex and bathing; the thin and weak, and persistent worriers; babies, women and young people; and corpulent people with a ruddy complexion. However those with dry bodies, purged of waste matter, who adopt a sensible and suitable regimen, will succumb to the pestilence more slowly.