Poggio Bracciolini, Liber Facetiarum (199):
How to Avoid Cold:
“Once, when I asked how to avoid getting cold in bed, a certain bystander said to me, ‘In the way which my friend employed when he was a student. For, though he was always in the habit of clearing his bowels after dinner, he sometimes abstained from that practice, arguing that the shit which he held in heated his body at night.’ This is a remedy for cold which has fallen out of use.”
Quaerenti aliquando mihi, quomodo frigus in lecto vitaretur: ‘Eo,’ quidam a circumstantibus ait, ‘quo socius meus dum vacaret studiis, utebatur. Nam cum semper solitus esset post coenam ventrem purgare, quandoque eo usu abstinebat, asserens retentum stercus calefacere noctu corpus. Remedium frigoris desuetum.