Scientific experiments disproving traditional theory of microbial generation

Microbiology & Spontaneous Generation

Microbiology is the study of microbes that are practically invisible to the human eye. Although microbes are usually associated with causing and aiding disease, they are essential organisms in the ecological world. They allow for life to thrive and are of great interests for food, scientific, and medical industries (Black, 2008). The term microorganism encompasses bacteria, protozoa, fungi, archaea, parasites, algae, prions, and viruses (Nester, Anderson, & Roberts, 2012). Each of these types of microorganism is responsible for everything that can essentially cause illness in living organisms, but are also necessary for the proper functioning of a mammal's digestive tract. However, in early scientific history, as illnesses were being investigated and the cell theory was beginning to emerge, the question about whether life could come out of nowhere was being explored. Because the majority of microorganisms were practically invisible, early microbiologists did not understand the concept of contamination and microbial growth. They instead attributed illness and spoiling to "vital forces" that initiated and allowed for these to develop; these seemed to stem from nothing, therefore, the theory of spontaneous generation was developed (Nester, Anderson, & Roberts, 2012).

In the beginning of the field of microbiology, the theory of spontaneous generation was believed to be true. This theory stated that life can arise from non-living matter (Nester, Anderson, & Roberts, 2012). In early philosophical history before any knowledge of the existence of microorganisms was popular, great thinkers such as Aristotle agreed with the idea that living organisms have the capacity of generating out of nowhere. He believed that nonliving matter gave rise to living organisms through the ability to spontaneously develop some form of life from nothing. This theory was proven over and over again when individuals looking for confirmation on their own rendition of spontaneous generation tested out this hypothesis.

Early scientists recognized that life seemed to arise from putrid or rotting matter (Black, 2008). For example, when maggots were first observed, it was believed that these small creatures arose from nothing when something or someone was exposed and dead. As soon as meat from animal or human flesh was left exposed for an extended period of time, maggots developed and flies grew. In order to prove the theory of spontaneous generation, John Needham designed an experiment where he boiled two broths that he then allowed them to cool down in two covered flasks (Nester, Anderson, & Roberts, 2012). Within a short period of time, microorganisms had infested both sealed flasks. He observed these results and concluded that the non-living liquid broth had itself created life (Black, 2008). Although scientists may have questioned the validity of this theory, not a large enough group existed to merit disproval. This was the case for centuries, until experiments disproving the theory of spontaneous generation arose.

As the popularity with the theory of spontaneous generation declined, scientists such as Francesco Redi set out to design an experiment that would prove that this theory was in fact a false representation of what was actually occurring. He wanted to prove that maggots, which were credited as being the proof of the existence of spontaneous generation, did not just spontaneously appear from rotting meat. In order to do this, Redi took two jars and filled them with meat that had rotted. One jar was left opened so that flies would have the opportunity to land on the meat and lay their eggs (Nester, Anderson, & Roberts, 2012). This is what Redi thought initiated the growth of maggots, not spontaneity. The second jar was sealed tightly so that nothing would be able to penetrate the jar and initiate growth. This in fact did occur. The jar that was sealed and never opened did not show any signs of life, while the one that was opened produced maggots and eventually flies (Nester, Anderson, & Roberts, 2012). However, these results did not convince skeptics who argued that no growth occurred because air was a factor that was needed for life, and Redi deprived the jar of air, so as a rebuttal, Redi designed a subsequent experiment where he covered the previously sealed jar with a thin net. Although air was able to get in, the net prevented the flies from coming in contact with the meat, and therefore no life arose (Black, 2008). This was the first experiment that completely disproved spontaneous generation.

After the experiments aforementioned were conducted, scientist Lazzaro Spallanzani maintained the idea that air had entered Needham's flask, and the air was what had contaminated the broth, allowing for the microorganisms to grow and flourish, and not that life had come from the broth itself. Although the broths were heated, Spallanzani thought that not enough heat had been applied to kill any microorganisms and once the broths had cooled down, the exposure to air caused for life to develop (Black, 2008). He solved this problem by designing a repeat of the experiment first implemented by Needham, but heated the broth after they had already been poured in the flask. By applying enough heat, life did not arise. It was still argued however, that the heat had killed the "vital force" that was needed for life to arise (Nester, Anderson, & Roberts, 2012). This second experiment disproved spontaneous generation, but still left doubts in the minds of scientists.

It was Louis Pasteur that finally designed an experiment that completely disproved the theory of spontaneous generation. His thought was that the air contained and carried life, such as microorganisms, that would initiate growth (Black, 2008). He boiled numerous short-neck flasks with broth. Some were left sealed, while others were left opened. After days of exposure to oxygen, those that were not sealed had an abundance of growth, while life was nonexistent in the flasks that were sealed. In order to differentiate his experiments from Needham's, Pasteur then took long-neck flasks and shaped their necks into an S-shape. This allowed for air to be able to enter the flask, but because of the unique design of the flask, the microorganisms themselves were unable to penetrate into the broth; they would instead get stuck in one of the S-loops of the neck (Nester, Anderson, & Roberts, 2012). Pasteur was able to leave his flask out like this for months and no microbial growth was observed. However, upon removing the neck and exposing the contents of broth directly to the air, growth was present in just a couple days (Nester, Anderson, & Roberts, 2012). Pasteur concluded that what in fact caused growth was not the air itself, but the microbial particles in the air. This experiment finally provided the proof necessary to disprove the theory of spontaneous generation.