Image of two facing pages of the illuminated manuscript of "Isagoge", fols. 42b and 43a. On the top of the left hand page is an illuminated letter "D" - initial of "De urinarum differencia negocium" (The matter of the differences of urines). Inside the letter is a picture of a master on bench pointing at a raised flask while lecturing on the "Book on urines" of Theophilus. The right hand page is only shown in part. On its very bottom is an illuminated letter "U" - initial of "Urina ergo est colamentum sanguinis" (Urine is the filtrate of the blood). Inside the letter is a picture of a master holding up a flask while explaining the diagnostic significance of urine to a student or a patient. HMD Collection, MS E 78.
Ironically, the manuscripts that were being most carefully preserved in the libraries of Antiquity are virtually all lost. Papyrus has a life of at most a century or two in relatively moist Italian or Greek conditions; only those works copied onto parchment, usually after the general conversion to Christianity, have survived, and by no means all of those.