Cupping. Historical artwork showing the use of suction cups, a form of traditional medicine used to bring 'bad blood' to the surface from internal organs. The usual method is to heat a cup (here, a glass flask) and then apply it to the affected area (here, the buttocks). The air contracts as it cools, forming a partial vacuum, drawing blood to that area of the skin. The practice is thousands of years old, but is not thought to be effective and is not used in modern medicine.