III. Where are They Coming From ?

Following Leeuwenhoek`s discovery, although there no bursts of activity, some scientist minds did have the curiosity to determine the animalcules, found to be present in many different object, were coming from. Society had just emerged from Renaissance period and science, known as experimental philosophy, was in its infancy. The theory of spontaneous generations, i.e., the generation of some from of life from nonliving objects, had many strong followers among the educated and elite class. Since the time of the Greeks, the emergence of maggots from dead bodies and spoiled flesh was thought to be due to spontaneous generation. But around 1665, Redi disproved that theory by showing that the maggots in soiled meat and fish could only appear if flies were allowed to contaminate them. The advocates of spontaneous generation theory argued that the animalcules could not regenerate by themselves (biogenesis), but they were present in different things only through abiogenesis (spontaneous generation). In 1749, Needham showed that boiled meat and meat both, following storage in covered flasks, showed the presence of animalcules within a short time. This was used to prove the appearance of these animalcules by spontaneous generation. Spallanzani (1765) showed that boiling meat infusion in broth in a flask and sealing the flask immediately prevented the appearance of these microscopic organisms and thus disproved Needham`s theory. This was the time when Antonie-Laurent Lavoisier and his workers showed the need of oxygen for life. The believers of abiogenesis rejected Spallanzani`s observation, suggesting that there was enough vital force (oxygen) present in sealed flask for animalcules to appear through spontaneous generation. Later, Schulze (1830; by passing air through acid). Theodore schwann (1838; by cotton) showed that bacteria failed to appear in boiled meat infusion even in the presence of air. Finally, in 1864, Louis Pasteur demonstrated that, in boiled infusion, bacteria could grow only if infusions were contaminated with bacteria carried by dust particles in air. His careful and controlled studies proved that bacteria were able to reproduce (biogenesis) and life could not originate by spontaneous generation. John Tyndall, in 1870, showed that in a dust-free box, boiled infusion could be stored in dust-free air without microbial growth.