CHEWING-BALLS, a kind of balls made of aſafœtida, liver of antimony, bay-wood, juniper-wood, and pellitory of Spain; which being dried in the ſun, and wrapped in a linen-cloth, are tied to the bit of the bridle for the horſe to chew: they create an appetite; and it is ſaid, that balls of Venice treacle may be uſed in the ſame manner with good ſucceſs.
Source: wiktionary