Carl Linnaeus, The Lapland Journey, translated by Peter Graves (Edinburgh: Lockharton Press, 1995), p. 195.
Northern Husbandry, 30/09/1732, ¶1149:
Finnish “lura” is made like any other drink except that it is not boiled. Red-hot stones are thrown into it instead, and it is from this that it gets its purgative effect, which is similar to that of iron.