A Marvelous Treatise on Waters which master Petrus Hispanus composed with natural industry guided by the intellect is found in a number of manuscripts. Sometimes it appears to be the closing part of his treatise on diseases of the eyes,[1651] and its first item is “a marvelous water to preserve and clarify the sight.” But it also is found as a separate treatise, in which directions are given for distilling various liquids, which in at least one manuscript are accompanied by two figures of chemical apparatus.[1652] In another manuscript the word philosophus is substituted for master Petrus Hispanus in the title given at the beginning of this paragraph, but the treatise is presumably the same.[1653] In this case, at least, it seems to include exactly twelve waters[1654] and so to conform to other medieval books Of twelve waters, of which we treat further in another chapter.[1655] Also its last two “waters” are an elixir of life and alcohol.[1656] If Peter of Spain came from Compostella, he may have had something to do with a Book of Compostella, which treats of many waters and of many oils and of many salts of great virtue. However, Brother Bonaventura, a Franciscan, is said to have composed the book in the convent of the Brothers of St. Mary in Venice.[1657]
Other works ascribed to him.
A Rule of Health[1658] and a Rule of Safety through all the months,[1659] which are ascribed to Peter in still other manuscripts, very likely have some connection with the above-mentioned Summa de conservanda sanitate or with the Letter to Frederick on the Rule of Health which has also been mentioned earlier in this chapter. A treatise on anatomy is attributed to Peter in an Italian manuscript,[1660] and a Book of Life and Death and of the Causes of Longevity and Brevity of Life is listed as his in an Oxford manuscript.[1661] Perhaps the shortest work ascribed to him is one of seven verses on rain.[1662] Commentaries by him on one or more of the following works are contained in a manuscript at Paris:[1663] the Introduction of Johannitius (Honein or Hunain ibn Ishak) to the Ars parva of Galen, the Prognostics of Hippocrates, Philaretus concerning the pulse, Theophilus on urines, the Aphorisms of Hippocrates, the Microtegni itself. A Liber naturalis de rebus principalibus naturarum is ascribed to Peter in a Vienna manuscript.[1664]
Commentaries on Isaac’s Diets: their scholastic method.
We come finally to Peter’s Commentaries upon the works of Isaac on Universal Diets and Particular Diets.[1665] They are as full as the Thesaurus pauperum was abbreviated and as scholastic and dialectical in form as it was empirical. Where Isaac’s text is clear Peter leaves its meaning to the reader’s industry,[1666] but it suggests to him over a thousand further questions which he takes up one after the other, listing authorities pro and con in each case and rebutting or reconciling them. Here we see the handiwork of the author of the favorite manual of logic of the later middle ages. The systematic, but abstract, sophistical, and jejune character of this method may be sufficiently illustrated by quotation of the closing passage of the “First Lecture” (Lectio prima).[1667]
“Next we proceed to the fourth point and inquire whether any food can be found of like nature to our bodies. And it would seem so, since when foods are called temperate and equal, they are not called equal except with respect to the body. But certain foods, such as chicken meat and the like, are called temperate and equal; therefore it is possible to find food of like nature to our bodies.”
“Against this three arguments are advanced. The first is that it is impossible to associate or join two different individuals; therefore a plant which grows in the earth and an animal cannot be joined and made one. The second argument is that nothing which is at first contrary and at last similar is of like nature to our bodies; but such is food, according to Aristotle, therefore no food is at all like. The third argument is that nothing far removed from human nature in constitution and composition and species is in any way like human nature. But all food is of this sort; therefore no food at all resembles the nature of our bodies, which we concede.”
“But it should be said anent these opposing arguments that ‘like’ may be understood in two senses. Either it means alike in all respects, and so no food is like. In the second sense, it means that it makes no manifest impression on the body, and in this sense some foods are called of like nature, such as chicken.”
“Next it is asked whether human flesh is nourishing, since nutriment goes by likeness. And it would seem so, for Isaac says that man is not nourished by the elements, since he is too far removed from them. Therefore that flesh which approaches closest to human nature should be the most nutritious. But this is human flesh; hence human flesh should be very nutritious. Here is another argument. Nutriment is from likeness, and from equal nutriment comes a well-balanced state of health; now the human constitution is especially temperate and well-balanced; therefore it requires temperate and equal food, and such, some agree, is human flesh. We, however, call it the worst sort of nutriment for two reasons: one, its corrruptibility; the other, its excessive unctuosity. For as the flesh of the body endures by virtue of the presence of the soul, so after the spirit’s departure the flesh becomes moist, vile, and fetid; and herein lies the solution of the difficulty, since if it is temperate, it has this property from the soul while it exists in the body.”
As to what the effect would be of eating men alive, Peter does not state. His argument may have possessed an additional interest for his own time from the possibility of applying it in theological as well as medical matters,—for example, the sacrament of the Eucharist.