Complex sentence: The doctrine of signatures, dating from the time of Dioscurides and Galen, states that herbs that resemble various parts of the body can be used by herbalists to treat ailments of that part of the body.
Split into simpler sentences: The doctrine of signatures is a philosophy shared by herbalists from the time of Dioscurides and Galen. This doctrine states that herbs that resemble various parts of the body can be used to treat ailments of that part of the body.