This free textbook is a Wikibook, which means that the content is constantly changing. The word physiology is from the Ancient Greek φυσιολογία (phusiología, "natural philosophy") and it is the study of how organisms perform their vital functions. An example is the study of how a muscle contracts or the force contracting muscles exert on the skeleton. It was introduced by French physician Jean Fernery in 1552. Physiology is built upon a tripod of sciences: physics, chemistry, and anatomy.