(Chapter 39) Footnote 18:

Possibly from smallpox, which was frequently epidemic in early modern Europe. See Hopkins 1983, pp. 27-32. Girolamo Fracastoro’s De contagione (1546) gives evidence of the endemic presence of smallpox in Italy at this time. Olive oil is still recommended in the treatment of smallpox lesions. See Dixon, 1962 pp. 101f. Ointment made from human fat was also a famous witchcraft ingredient. For a recipe, see G. Cardano De subtilitate 18 (Opera 3:639). We are grateful to Nancy Siraisi for this reference.