In medieval medicine, humoral medicine was a common practice. (For more about the humors, see my earlier post here.) When patients were ill, food and drugs – often plant-derived – were prescribed, taking into account not only the symptoms, but also his or her temperament, age, location, and time of year.
Balancing the humors seems to me to have been somewhat precarious at times. If one was too choleric (hot and dry), foods and herbs that were considered cold and moist were prescribed. However, too much could cause a swing in the opposite direction. Foods were assigned qualities similar to those of the four humors – for example, cucumbers and watermelons were considered cool and moist.
The degrees of coolness (or heat) and dampness (or dryness) varied; foods cold or hot in the first degree were prescribed for milder conditions; foods cold or hot in the fourth degree were generally toxic and used only in extreme cases. Opium was considered cold and dry in the fourth degree.
The author of De fructibus used numerous sources when writing his book. Nearly every entry (there are 27 fruits and herbs named in it) is separated into sections, detailing that particular food’s qualities as cited by classical authors (Galen, Avicenna, Averroès, etc.) and its uses in disorders of the stomach, liver, kidneys, bladder, lungs, etc., and as poisons and cosmetics.
Below is the loosely translated first section for cucumbers and watermelons, fruits with which one can keep cool in the heat of summer:
Rasi wrote in [his Liber] Almasoris that the watermelon and cucumber are exceedingly cold in the third degree. Melon and cucumber are cold, but less damp. Averroès, in the second book of Colliget, stated that the cucumber is cold and damp in the second degree. He wrote much about the cucumber, but did not mention [that] watermelon is cold. In his own [works], Galen says the same, simply, [that] the cucumber is cold and damp in the second degree and the watermelon is less cool. In Alimentus, Galen says the cucumber is less damp than watermelon. Avicenna, in the second book of the Canon, says [that] the cucumber is cold and damp in the second degree.
Sources:
Anderson, E.N. “Food and Traditional Medicine.” In Everyone Eats: Understanding Food and Culture, Second Edition. New York: NYU Press, 2014.
Editors of the Cloisters Museum and Gardens blog. “Cool, cooler, coolest.” The Medieval Garden Enclosed blog. The Cloisters Museum and Gardens, The Metropolitan Museum of Art. 27 July 2012.