Pathology is the science that studies the nature of diseases and the changesthey 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 thebody), 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 leadersand obstructed progress in the study of anatomy and pathology through the Middle Ages. By the Renaissance, however, reports from post-mortem dissectionsbegan 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 they dissected cadavers. But Fernel still held to the ancient teachings of the humors.
In the 18th century, the anatomical basis of disease began to emerge. Publichospitals provided a seemingly endless supply of corpses for dissections after death, and hospitals became centers for teaching and practicing morbid anatomy (the abnormal structures in the body associated with disease). By the second half of the 18th century, in both America and Europe, surgeons and physicians had already begun to correlate signs and symptoms of patients with findings from autopsies after the patients died.
In 1761, Giovanni Battista Morgagni (1682-1771) published the first textbookto systematically detail morbid anatomy and to locate diseases within individual organs. But humoral theories remained firmly entrenched, and the study ofanatomy was still limited to what pathologists could observe of organs, muscles, and bones with the naked eye. All the same, as a result of their investigations into corpses, pathologists in many different countries were beginningto ask questions about what made a tumor benign or malignant, the nature ofpus, how wounds heal, and whether blood clots are beneficial or harmful.
Major progress was quick to follow. In France, Marie François Xavier Bichat (1771-1802) studied tissues rather than organs. One of his important contributions was the announcement that the disease of a tissue is the same nomatter which organ the tissue is in. Bichat worked without the aid of a microscope. But the introduction of improved compound microscopes in the 1820s made it possible to study both normal and diseased tissue more extensively and more accurately than ever before. In 1858, Rudolf Carl Virchow (1821-1902) proved conclusively that diseases arose in the cells of organs and tissues, notin the organs and tissues generally. Not long after, the investigations of Louis Pasteur (1822-1895) and Robert Koch (1843-1910) into bacteria were a major step in rounding out understanding of how disease works.
By the end of the 19th century, pathology had come into its own as a separatemedical specialty. Today, pathologists perform, evalute, or supervise diagnostic tests, using materials from living or dead patients. Their work is mostly carried in the laboratory, and they work closely with physicians who are directly in charge of patients. Among the materials a pathologist examines (inprocedures generally known as biopsies) are surgically removed body parts, blood and other body fluids, urine, feces, and so on. Pathologists also practice autopsy, which allows them to reconstruct the end of the physical life of adead person by providing information about the workings of disease they would not be able to get any other way. It is not possible for any one person toknow all there is to know about pathology, so pathologists who specialize inone area or another frequently work together. For example, pediatric pathology studies disease processes in children. Forensic pathology is a subspecialtywhose goal is to clarify crimes or legal issues.
Advances in laboratory techniques and increasingly fine-scaled instrumentation have greatly expanded the information available to the pathologist in determining the causes of disease. Research in genetics is also changing the studyof pathology. More and more, pathologists are being called on to examine themolecular structure of DNA and to identify molecular markers of disease, aswell as to study the impact of environmental factors on heredity.
Training in pathology requires a medical degree and roughly five years of postgraduate study.