What is Pathology (from Encyclopedia Brittanica) 

Medical specialty concerned with the determining causes of disease and the structural and functional changes occurring in abnormal conditions. Early efforts to study pathology were often stymied by religious prohibitions against autopsies, but these gradually relaxed during the late Middle Ages, allowing autopsies to determine the cause of death, the basis for pathology. The resultant accumulating anatomical information culminated in the publication of the first systematic textbook of morbid anatomy by the Italian Giovanni Battista Morgagni in 1761, which located diseases within individual organs for the first time. The correlation between clinical symptoms and pathological changes was not made until the first half of the 19th century.

The existing humoral theories of pathology were replaced by a more scientific cellular theory; Rudolf Virchow in 1858 argued that the nature of disease could be understood by means of the microscopic analysis of affected cells. The bacteriologic theory of disease developed late in the 19th century by Louis Pasteur and Robert Koch provided the final clue to understanding many disease processes.

Pathology as a separate specialty was fairly well established by the end of the 19th century. The pathologist does much of his work in the laboratory and reports to and consults with the clinical physician who directly attends to the patient. The types of laboratory specimens examined by the pathologist include surgically removed body parts, blood and other body fluids, urine, feces, exudates, etc. Pathology practice also includes the reconstruction of the last chapter of the physical life of a deceased person through the procedure of autopsy, which provides valuable and otherwise unobtainable information concerning disease processes. The  knowledge required for the proper general practice of pathology is too great to be attainable by single individuals, so wherever conditions permit it, subspecialists collaborate. Among the laboratory subspecialties in which pathologists work are neuropathology, pediatric pathology, general surgical pathology, dermatopathology, and forensic pathology.

Microbial cultures for the identification of infectious disease, simpler access to internal organs for biopsy through the use of glass fiber-optic instruments, finer definition of subcellular structures with the electron microscope, and a wide array of chemical stains have greatly expanded the information available to the pathologist in determining the causes of disease. Formal medical education with the attainment of an M.D. degree or its equivalent is required prior to admission to pathology postgraduate programs in many Western countries. The program required for board certification as a pathologist roughly amounts to five years of postgraduate study and training.