Pathology is the science that studies the nature of diseases and the changes they produce in the body.

Since ancient times, physicians have concerned themselves with the distinguishing features of health and disease. Until the early 19th century, however, their ideas were based on a theory of humors (that is, elemental fluids in the body), rather than systematic examination of body parts and disease processes. Disease was believed to result from an imbalance of these humors. Dissection of dead bodies to learn about disease was not allowed by religious leaders and obstructed progress in the study of anatomy and pathology through the Middle Ages. By the Renaissance, however, reports from post-mortem dissections began to provide a new and important source of information contributing to medical knowledge. In his Universa medicina, Jean François Fernel (1497-1558) introduced the term pathology to describe the abnormalities detected by anatomists when...