From The Long Lost Friend:
Wen on Horse
Take any bone which you accidentally find, for you dare not be looking for it, and rub the wen of the horse with it, always bearing in mind that it must be done in the decreasing moon, and the wen will certainly disappear. The bone, however, must be replaced as it was lying before.
The grimoire The Long Lost Friend lists this spell.
Timeline of related events
1820Publication of Hohmann's Long Lost Friend (lists this spell)