Chinese pharmacy. Herbalist measuring out remedies using weighing scales at a traditional Chinese pharmacy in Vietnam. Herbalism is a system of medicine in which plants are used to promote health and treat symptoms. Chinese medicine is based on the theory of a universal bodily life force, called Qi. This is balanced by two complimentary forces, yin and yang. Imbalances in these forces disrupt the flow of Qi, causing illness. Chinese medicine therefore aims to rebalance yin and yang. Photographed in Hanoi.