Pathology can be traced back to what ?
In the 19th century , physicians realized that disease - causing pathogens , or germs ( disease - causing , or pathogenic , microbes , such as bacteria , viruses , fungi , amoebae , molds , protists , and prions ) existed and were capable of reproduction and multiplication , and that evil spirits or humors , or even the signs and symptoms of the condition , were not the causative agent of a disease .