Sources : Louse

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Worms 9.35): Lice [pediculi], as the Liber rerum says, are called from the number of feet: for they have of innumerable feet [pedes]. This evil is created from the very flesh of man, and although this is indubitable, yet the creation of lice is invisible. Some say that these are invisibly produced by the sweat of man, others by pores and evaporations. Against these the chief remedy, as the Philosopher says, is frequent washing of the body with sea-water or more vigorously with salt; or quicksilver [mercury] boiled for a long time in olive oil and a girdle dyed from this, or egg white and quicksilver more carefully tempered and a woolen girdle dyed from this and worn; or to wear butter mixed with quicksilver, and clothes infused with it. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book18.87): A Lowce is called Pediculus, and is a worme of the skinne, and hath that name of Pedibus, the féete, as Isido[re] sayth lib. 12. And grieveth more in the skinne with the féete and with créeping, then hée doth with biting, and is gendered of right corrupt aire & vaporous, that sweate out betweene the skinne and the fleshe by pores, as Constantine sayth in Viatico. Oft as he sayth, lice and nits gender in the head or in the skinne, and come of purgations, which kinde casteth out, and maketh them fast betwéene the flesh and skinne upon that place. And expositours say, that some lice gender of sanguine humour, and be red and great, and some of fleumatike humours, and they be softe & white, and some of cholarike humours, & be citrine, long, swifte, and sharpe: some of melancholike humour, and they bée couloured as ashes, and bée leane and slow in mooving. And where great multitude of Lice is in a bodye that is right full and corrupt, it is oft token of general corruption, as of Morphea, or of Lepra, as hée sayeth. Against the grieving of lice, oft washing, combing, and medicinall cleansing of the head helpeth, For as Constantine sayeth, quicke Silver with ashes of willowes, slayeth them, & namely if they be gendred of hot humour, & so doth Lead burnt with oyle and vineger, & if they be gendred of cold humour, then helpeth Staphisagra & Auripigmentum, with oyle and vineger, & so doth sea water, and water of salt Welles. And as there be diverse kinde of beastes, so in the¯ be diverse manner of lice, as it fareth in hogs, his louce is called Usia, and hath that name because he burneth, for where hée biteth, the place burneth so, ye blaines arise there, as Isidore sayth, lib. 12. And the leaner that a louce is, the sharper the biteth and gréeveth. - [Batman]