The Germ Theory of Disease. In the nineteenth century when the distribution of microscopes became widespread, the sheer degree of microbial life forms was more apparent and thus the two questions Does spontaneous generation occur? a
The Germ Theory of Disease
Although the germ theory of disease is mainly accredited to Louis Pasteur for his work in disproving the theory of spontaneous generation, to Robert Koch for developing the criteria required to ascertain whether a microorganism has caused a certain disease (Koch’s postulates), and to Joseph Lister for the introduction of antiseptics into surgery, a whole host of other scientists have contributed both directly and indirectly to the establishment of the theory (Snowden 2010).
In the nineteenth century when the distribution of microscopes became widespread, the sheer degree of microbial life forms was more apparent and thus the two questions – “Does spontaneous generation occur?” and “What is the nature of infectious disease?” emerged (Madigan M. T. et al. 2009. pp. 10-11). The answering of these questions would lead to what would become the basis of the germ theory of disease.
Question 1 – “Does spontaneous generation occur?”
Many scientists have worked on and contributed to answering this question. In 1668, Francesco Redi, proved that the popular belief that maggots arose spontaneously from rotting meat was false. Even though this was on a much larger scale than disease causing microorganisms, the basic principle which would later be applied was the same. Redi did this by setting out meat in a variety of flasks, with varying degrees of coverings, from being completely open to the air to being fully sealed, he did this experiment in order to prove his theory that maggots developed from eggs that were laid by flies. After his experiment he concluded that maggots only emerged from the flasks the flies could reach the meat and lay their eggs, proving his hypothesis correct (Evers C. and Levine R. 2009). However, even after the success of this experiment, the theory of spontaneous generation was still widely accepted. The next person to make a significant challenge to the spontaneous generation theory was not until 1765 when Lazzaro Spallanzani set out an experiment to counter the experiment done in 1745 by John Needham. In Needham’s experiment he heated broths, and transferred them into covered flasks, believing all of the microorganisms were killed by boiling, thus when they were cooled and were found to be turbid with microorganisms, he deemed it was evidence enough to prove that spontaneous generation did indeed occur. Spallanzani however believed that microorganisms were only present due to some contamination and so set out a similar experiment but he heated the flasks after they were sealed, eliminating any chance of contamination, and, as Spallanzani thought, no microorganisms were present. When Needham was proven wrong, he countered with the argument that all the experiment proved was that spontaneous generation could not occur without ‘fresh air’. (Evers C. And Levine R. 2009.; Kusintiz M. 2011.) The final conclusive proof that the theory of spontaneous generation was incorrect came from Louis Pasteur’s experiment with the swan necked flasks in 1864. The brilliance of his experimental design meant that he could disprove the theories of spontaneous generation completely, even fresh air being a requirement. He was able to do this because of the specific shape of the flask which allowed cooled air to re enter the flask, but the ‘neck’ was bent in such a way that microorganisms from the surrounding air remained in the bend and were unable to fall into the flask and contaminate the liquid inside. The steps of the experiment were as follows:
