<P> In 1720, Richard Bradley theorised that the plague and' all pestilential distempers' were caused by' poisonous insects', living creatures viewable only with the help of microscopes . </P> <P> In 1762, the Austrian physician Marcus Antonius von Plenciz (1705 - 1786) published a book titled Opera medico - physica . It outlined a theory of contagion stating that specific' animalculae' in the soil and the air were responsible for causing specific diseases . Von Plenciz noted the distinction between diseases which are both epidemic and contagious (like measles and dysentry), and diseases which are contagious but not epidemic (like rabies and leprosy). The book cites Anton van Leeuwenhoek to show how ubitquitous such animalculae are, and was unique for describing the presence of germs in ulcerating wounds . Ultimately, the theory espoused by von Plenciz was not accepted by the scientific community . </P> <P> The Italian Agostino Bassi was the first person to prove that a disease was caused by a microorganism when he conducted a series of experiments between 1808 and 1813, demonstrating that a "vegetable parasite" caused a disease in silkworms known as calcinaccio--this disease was devastating the French silk industry at the time . The "vegetable parasite" is now known to be a fungus pathogenic to insects called Beauveria bassiana (named after Bassi). </P> <P> Ignaz Semmelweis, a Hungarian obstetrician working at the Vienna General Hospital (Allgemeines Krankenhaus) in 1847, noticed the dramatically high maternal mortality from puerperal fever following births assisted by doctors and medical students . However, those attended by midwives were relatively safe . Investigating further, Semmelweis made the connection between puerperal fever and examinations of delivering women by doctors, and further realized that these physicians had usually come directly from autopsies . Asserting that puerperal fever was a contagious disease and that matter from autopsies were implicated in its development, Semmelweis made doctors wash their hands with chlorinated lime water before examining pregnant women, thereby reducing the mortality rate from 18% to 2.2% at his hospital . Nevertheless, he and his theories were rejected by most of the contemporary medical establishment . </P>

When was the germ theory proposed and on what basis