Pathology derives from pathos (disease ) and logos ( study ). Literally meaning "the study of disease". Pathology emphasized four aspects of the disease process. These are the cause (etiology), the mechanism of development (pathogenesis), the alterations of structure and forms (morphology) and functional alterations (pathophysiology). Due to advances and increased complexity of medical sciences, pathology has many branches as clinical medicine. For academic purposes, Pathology has been divided in general and systemic (organ) pathology. Modern pathology has its origin in the cellular studies carried out by the German doctor Rudolf Virchow. After Virchow, cellular adaptations and changes secondary to disease processes have been the main study subject of this medical science.