Plants and animals help keep the soil fertile. Plant roots tunnel through the soil and break it up, and decaying plants form humus. Burrowing animals mix the soil; the excrete of animals contribute nutrients and improve soil structure.
Chinese medicine is a system of medicine partly based on the idea that an energy, called qi (say chee), flows along pathways in the body called meridians. In this belief, if the flow of qi along these meridians is blocked or unbalanced, illness can occur.
Two concepts that are unique and fundamental to Chinese medicine are Qi (usually translated as vital energy) and yin and yang (the harmony of all the opposite elements and forces that make up existence).