II. Discovery of Microorganisms

The discovery of microorganisms ran parallel with the invention and improvement of microscope. Around 1658, Athanasius Kircher reported that using a microscope, he had seen minute living worms in putrid meat and milk. The magnification power of his microscope was so low that he cloud not have seen bacteria. In 1664, Robert Hooke described the structure of molds. However, probably the first person to see different types of microorganisms, especially bacteria, was the Dutch businessman turned naturalist Anton Van Leeuwenhoek, using microscope that probably have not above 300x magnification power. He observed bacteria in saliva, rain water, vinegar, and other material, sketched the tree morphological groups (spheroids or cocci, cylindrical or bacilli, and spral or spirillia), and also described some to be motile. He called them animalcules and in 1675 reported his observation to the newly formed leading scientific organization, The Royal Society of London, were his observation were read with fascination. As fairly good microscopes were not easily available at the time, during the course of next 100 years, other interested individuals and scientists only confirmed Leeuwenhoek`s observations. In the 19th century, as result of the Industrial Revolution, improved mind to see and describe creatures they discovered under microscope. By 1838, Ehrenberg (who introduced the term bacteria) had proposed at least 16 species in four genera and by 1875 Cohn had developed the preliminary classification system of bacteria. Cohn also was the first to discover that some bacteria produced spores. Although, like bacteria, the existence of submicroscopic viruses was recognized in the mid-19th century, they were observed only after the invention of electron microscope in the 1940s.