Hi, let us study in detail the debate over spontaneous generation. In 1668, based on Lewin Hook's observations, they Dahlia naturalist, Francisco already performed one of history's first control biological experiments, in which he placed rotting meat into jars with or without lids. To answer the question he had, can maggots be spontaneously generated from decomposing meat? Ready predicted that if flies were prevented from getting in contact with the rotting meat, there would be no eggs and therefore no maggots would hatch. Now let's see what actually happened. To demonstrate his experiment ready first placed rotting meat into six sets of jars.

He left the first two sets Oh open, allowing flies to enter the jar. He tightly sealed the next two sets of jars with lid and he covered the last two sets of jars with the cloth netting. In the controls with the open jars, the flies were able to lay eggs on the rotten meat, which then became maggots. Whereas in the other two sets of jars, the flies were unable to come in, and thus, there were no eggs or maggots present on the meat. So the results that we obtained were exactly as he predicted. This experiment demonstrated that spontaneous generation could not produce large living creatures such as maggots.

But what about the spontaneous generation of not large but minuscule organisms? JOHN Needham was a British priest and naturalist who, in 1748, suggested that micro organisms were generated spontaneously by a vital force that actually reorganize the decaying matter originated from more complex organisms such as lamp. To prove his point he placed mutton broth in tubes, and then boil the same and seal the tubes with corks. After waiting for several days, he described what happened next in the following matter the gravy swarm with life with microscopic animals of most dimensions as shown here. So he was convinced that putrefaction was able to generate the vital force that was needed for spontaneous generation of micro organisms. Now, because experiments can have different results based on different conditions, and Italian priest and naturalist named Lazarus fallen Zani challenged NIAMS conclusions by suggesting that the duration of heating might not have been long enough to kill all microorganisms.

So, in 1765, he repeated Needham experiments, but boil the tubes for a longer time. As control falls, he left some tubes open to air. But for the experimental groups he sealed some of the tubes loosely and others tightly. He described his conclusions as follows the number of Omni Masekela developed is proportional to the communication with external air, which means the more contact with air, the more microorganisms were present. Also the tubes that spell and Zani heated and seal did not have any microorganisms, whereas the tubes that need them heated and seal had growth of microorganisms, showing the importance of heating the tubes for a long period of time. Now after carefully scrutinizing spell and xanies experiments, Nerium and other nationalists argued that excessive heating must have destroyed the vital force of life.

Also, according to them, the tubes spell and Zani had were excluded from air which was necessary for generation of life. This debate over spontaneous generation continued until the mid 1800s. To get to a resolution, the French Academy of Sciences set up a contest for the best experiment to prove or disprove spontaneous generation. To solve the problem, there was a need for a new experimental strategy as we will see in future lecture series based on his previous work with microorganisms. Lewis Bashir knew that his concept of biological activity of microorganisms was not compatible with the theory of spontaneous generation. Lewis pastor who was a professor of chemistry and the Dean of the Faculty of Sciences in the University of Lilly, France, took up the challenge of disproving spontaneous generation in 1859.

In order to do so, he set up two experiments, experiment one he divided into two parts, which we will identify by the plus plus K and V. Lewis posture, he'd sterilized both flasks with containing the broth for long enough time to kill all the microorganisms. Just as balance and he did, he left flask a open to air. Whereas floss B he sealed. He allowed time to pass for both plus. What he observed next was that the floss that was left open floss k had microorganisms growing in it as seen here. Whereas floss B that was sealed, contained broth that was sterile, devoid of any microorganisms.

Foster's conclusions at this point we're that the broth contains nutrients that help the growth of microorganisms in the air. his critics argue that it is the decomposed products in the broad that gave life through spontaneous generation. Buster also he killed the microorganisms in the air at the beginning of the experiments showing that microorganisms can grow in the broth at a later time if left open. But his critics argued that sealing the flask prevent the vital force needed for the spontaneous generation of microorganisms. So, experiment one was not enough to disprove spontaneous generation. Buster now had to come up with another experiment where air can be allowed to come into contact with abroad, and yet there would be no growth of microorganisms.

But how can he do that? Well, he found his solution in the use of flasks with a swan shaped neck as shown over here. This curved shape neck allows contact with air but inhibits the movement of particles. He hits sterilized three flass, which we can call as Class A, B and C. He left flask is standing still for a long period of time. He tilted Class B so that brought would enter the neck of the flask and he snapped off the neck of flask C as shown here. Esther's experiment to short several important conclusions.

Flask a was sterile, which means that dirt and microorganisms were being trapped at the curvature of the neck preventing them to reach to the flask which also means that clean air was reaching the broad plus V on the other hand was contaminated, which means the broth that entered the neck of the flask was exposed to micro organisms and that were in the air plus C was also contaminated. which happened when the neck of the floss was snapped off to allow air with dirt and microorganisms to enter in. With this elegant set of experiments pastor demonstrated that even though microorganisms are present in the air, they are not created by air. Air alone does not induce contamination, it just carries the contaminants. This final conclusion put an end to the long term debate over the theory of spontaneous generation Louis pastors experiments are a perfect example of the process of scientific inquiry.

Scientists answer questions and solve problems through this process also known as the scientific method, which is the way problems are investigated. It all starts with observations. We observe certain biological phenomena and make notes of the same. Next, we formulate questions such as What has happened? Why did it happen? And how did it happen?

When we come up with possible explanations, we call those as hypothesis. A hypothesis is a temporary explanation for an observed phenomenon that can be tested experiments that are set up to answer those questions. And to test the hypothesis are then then formulated. In the experiment, the only one variable is changed and all the other factors remain the same. In pasters experiment one for example, the floss were either opened or sealed. In both the control and experimental tubes, similar flasks were used.

The broth in both floss was the same, and the two flasks were both heated for the same length of time that I used to control in his experiment. It is basically a standard to compare to setting up comparative conditions. In his experiment, the floss that was left open was his control to the floss that was sealed now In science, a theory is a hypothesis that has been tested and shown to be correct every time by several investigators. So at some point there should be sufficient evidence to state that as hypothesis is a theory. However, theories are not written in stone that can be open to further investigation and experimentation and so they can be refuted. Now, a brief look at the topics that were covered.

We started with a history of microscopy with the major contributions of lens crafter Robert who can plot merchant Anton Van leeuwenhoek to the field of microscopy. Then we looked at the controversy over the origin of living things One of them was the doctrine of spontaneous generation, which was well accepted in those days. This precipitated a series of controversies and then set of experiments by several scientists, either for or against spontaneous generation. And then with an elegantly designed set of experiments, Louis paster ended the debate over spontaneous generation by disproving it once and for all, and thus proving the theory of biogenesis Omni vivo ex vivo meaning life comes from life.