(Chapter 4) Footnote 1:

Lat. Fuliginosa recrementa, reflects an idea common in Galen that the wastes of digestion and metabolism are comparable to those of combustion: “The wastes that we call as it were sooty, soot-dark, and smoky (ai)qalw/dh te kai\ lignuw/dh kai\ kapnw/dh) in the class of warmth, are all earthy (gew/dh) things, as it were half-digested in the natural heat, as smoke is by fire.” ( De difficultate respirationis 7.811.4). For the idea that sutures ventilate the brain, see Aristotle De partibus animalium 2.7 (653b1-3). See also Book II Chapter 5, where it is said the skin disposes of fuliginosa excrementa through the pores.