in this video, we're going to begin our lesson on the contradictory experiments conducted by john Need him and Lazaro Spa Lynn Zanni. Now first we're going to focus on john Needham's experiments. And then later in a different video, we'll talk about Lazaro's Palin Zanny's contradictory experiments. Now, the big takeaway of this video is that john Needham's results incorrectly supported spontaneous generation. And so john Need him was an english scientist and priest who tried to experimentally prove spontaneous generation. Although john need him was unaware that he had poor experimental setup and that he incorrectly believed that briefly boiling a broth would sterilize it and sterilization is the process of killing all microbes in a sample. And it turns out that brief boiling is not always enough to sterilize the broth, but he was unaware of that. And so in terms of john Needham's experimental results, after he had briefly boiled a flask of broth, incorrectly believing that it was sterile. Um and after allowing that broth the coal and sealing the broth with a cork need him, saw microbial growth in his flask with broth in it. And so uh john need him in terms of his conclusions, uh Need him had incorrectly concluded that his sterile flask of broth had spontaneously generated microbes. And again, he believed that his flask was sterile after briefly boiling it, but that was not actually the case. And so if we take a look at our image down below, we can get a better understanding of john Needham's experiment. And so John Needham, who is right here live from 1713 to 1781. And he conducted this experiment in 1745 and notice he's saying, look, I did it, I proved that spontaneous generation is real. However, he was unaware of his poor experimental setup. And so over here in this first part of the experiment, what you can see is that john Need him took a flask of broth and boiled the broth for a short amount of time, he briefly boiled the broth and so with brief boiling of the broth, he incorrectly thought that he was sterilizing it. And so that is the main point that we're saying here is that john Needham incorrectly believed that all microbes died with brief boiling, although that was not the case, then he allowed the broth to cool while it was uncovered and this also created the potential for contamination during this cooling period that he was unaware of, because he was unaware that microbes could exist in the air. Mhm. Uh Then what john Needham did was he sealed his flask with a cork and the cork is actually not the best way to seal the flask and prevent contamination. Uh And so the broth ended up developing microorganisms because if there were microorganisms in the broth, originally, they were not all killed or microorganisms could have entered into the flash during the cooling period, or microorganisms could have entered into the flask through this porous cork and contaminate the flask. And these were all situations that john Needham had not considered. And so the big takeaways of john Needham's experiment is that john Need him had incorrectly believed all microbes died with brief boiling. He incorrectly believed that a cork seal would prevent contamination and he ended up incorrectly concluding that his experiments supported spontaneous generation because he saw microbial growth here. But he didn't realize that the microbial growth could have come from uh poor experimental setup. And so um, it was not until later when another scientist of the name Lazaro spelling johnny realized that something wasn't right Uh, with uh John Needham's experiments. And so it was not until 1776 that the scientist, Lazaro span Zanny performed a set of experiments to contradict need hymns findings. And so although Needham had incorrectly suggested that microbes could spontaneously generate Lazaro span Zanni followed up contradicting his experiment and so we'll talk more about Lazaro spellings Arnie's uh, contradictory experiments in our next video. But for now, this here concludes our brief introduction to John Needham's experiment and how his results incorrectly supported spontaneous generation. So I'll see you guys in our next video.

in this video, we're going to focus on Lazaro Spa Alan Zanny's experiment and how his experimental results disproved spontaneous generation. And so Lazaro Spa Lynn Zanni Was an Italian physiologist in the 1700s who performed experiments that contradicted Needham's results and recall from our previous lesson video that need homes results supported spontaneous generation. And so Lazaro swollen. Zanni proposed that Needham's experiment was flawed and that there were many mistakes throughout his experimental setup and spelling johnny also proposed that living organisms do not spontaneously generate. Yeah, Now Lazaro swollen Zanny's experiment was very similar to need hymns experiment except there were a few key differences. And so one of those main differences is that in small. In zanies experiments, he had sealed his flask by melting the glass closed and so sealing the flash by melting it closed helped to prevent microbial contamination. And then the second main way that's pollen Zanny's experiment differed from Needham's is that spans any boiled his broth for a significantly longer period of time in comparison to need hymns brief boiling. And so if we take a look at our image down below, we can get a better understanding of spellings Arnie's experiment. And so notice over here, at the far left, we're showing you an image of Lazaro's pollen. Zani who lived from 1729 to 1799 and conducted this experiment in 1767. And so you can see here we have a flash that's filled with this liquid broth here and one of the main differences between Stalin Zanny's experiment and need him. His experiment is that spans um spans any sealed his flask by melting the glass closed. And so you can see that with this arrow here, the glass, the top of the glass is melted closed to prevent microbial contamination. And then the second main way that Lazaro's Fallon Zanny's experiment deferred is that Lazaro Small and Zanny boiled his broth for a significantly longer period of time in comparison to need hymns brief boiling and the longer boiling allowed for a greater chance of sterilizing the broth or killing all of the microbes in the broth. Because brief boiling does not really kill all microbes or is less likely to kill all microbes, whereas longer boiling is more likely to kill all microbes. And so what Stalin Zanni realizes that as long as there were no cracks in his glass that was sealed closed, there were absolutely no microorganisms that grew in his flask. However, he realized that if he intentionally introduced a small crack into the flask, that it created an opportunity for microbes to enter into the crack and contaminate the flask. And so by cracking the flask, the cracks in the flask allowed microorganisms to grow. And so you can see that there is microbial growth in the flash that has the crack in it. But as long as there's no crack, there was no microorganisms. And so that's exactly what we see here in the results for Stalin's on his experiment, Small in Zanny never, yeah, saw microbial growth and the sealed flasks and he only saw microbial growth in the flash that were cracked open and so small. And Zani was able to conclude from these results that microbes do not spontaneously generate because if they did spontaneously generate then you would expect microbes to spontaneously generate even in the flask that was sealed closed. And he also concluded that the cracked flasks would allow microbes to enter from the air. And so once again you can see that with the crack that he intentionally introduced into some of his flasks that the crack created an opportunity for microbes to enter and contaminate the bra. And so over here on this part of the image, we have some important conclusions from Stalin's armies experiment number one being that melting the flasks closed, help prevent contamination. And that was one of the main differences between Stalin's armies and Needham's experiment, number two was boiling the broth for a longer period of time, helped to kill all of the microbes to ensure that there were no microbes that would be able to grow. And then number three, cracked flash were contaminated by microbes in the air and number four, he was able to conclude that microbes in the broth did not spontaneously develop or spontaneously generate because they did not generate in his sealed flats. And so overall Stalin Zanni helped to disprove spontaneous generation. Now there were still some opposers to Stalin's on these experiments. And opposers, they claim that spans on is sealed flask excluded some unknown vital source from the broth that was needed for spontaneous generation. And so basically what they opposers were suggesting is that the sealed flask just prevented some unknown vital source uh such as maybe oxygen, for example, from entering into the flask. And so that is what was preventing spontaneous generation. That's what the opposer said. And so uh there was still some skepticism even after spawns on these experiment, and some people still believed that spontaneous generation was likely. And so it was not until another scientist of the name of louis Pasteur came around to uh set up another experiment that finally disproved spontaneous generation once and for all. But for now we will talk about uh louis Pasteur's experiments later in a different video, but this concludes our introduction to spell in zanies experiment and how his results disprove spontaneous generation. So, I'll see you all in our next video

in this video, we're going to do a side by side comparison of john Need hymns and Lazaro swollen Zanny's experimental design. And so once again, Lazaro's Palin Zanny's experiments differed from John Needham's experiments in two significant ways. Number one, Lazaro's Palin Zanni completely sealed the flasks by melting the flasks closed before he boiled the broth in the flask. And this is important because this helped to ensure that no microbes could enter into the broth after boiling the broth. Now, the second significant way that's Palin Zanny's experiment differed from John Needham's is that's Palin Zanny boiled the bras for a significantly longer period of time and a longer boiling time helps to ensure that all of the microbes were killed by the heat, whereas shorter and brief boiling, like what need him did may not necessarily kill all of the microbes. And so there may still be some lingering microbes in the broth. And so if we take a look at our image down below, notice that the top half of the image is focused on john Needham's experiment. Whereas the bottom half of the image is focused on Lazaro swollen Zanny's experiment. And so uh focusing on john Needham's experiment first notice that need him did not seal the flask by melting it closed and so the flash remained open to the environment also, uh he only boiled his broth for a brief period of time, a short period of time and short boiling times may not necessarily kill any microbes that might be in the broth originally. Um and so there could be some lingering microbes even after a short period of boiling. Also, he allowed the broth to cool for a short period of time, which allowed for the opportunity for microbes to enter the flask from the air and contaminate the flask after boiling. And so where need him thought that his flask was going to be sterile. It turns out that he was incorrect because uh there could have been lingering microbes, or the microbes could have contaminated the flash from the air. Also, john Needham sealed his flasks by using a cork which is porous and a porous cork, a meaning that has pores in it and has holes in it, allows for microbes to be able to pass through the cork and enter into the flask. And so here we're showing you how microbes can enter through the porous cork and still contaminate the flask. And so where john need him, saw microbial growth and attributed it to spontaneous generation. He was incorrect because those microbes could have come from either being lingering microbes after short boiling times, or microbes that simply just entered into the flask from the air. And so in, at the end of john Needham's experiment, the microbes were present. and that's why he uh suggested spontaneous generation of the microbes, but he was incorrect because he didn't realize how many flaws there were throughout his experiment. Now, down below, we're showing you swollen Zanny's experiment, which you can see that he sealed his flask by melting the glass closed and melting the glass helped to prevent contamination throughout his experiment. Then he boiled his broth for a significantly longer period of time, which helped to ensure that all of the microbes that may have been existing in the bra were killed and that his broth was actually sterile. And so uh what you can notice is that in Stalin's on these experiments, the microbes were absent and because the microbes were absent, uh he suggested that spontaneous generation was not the way for microbes to um develop. And so you can see there's no spontaneous generation here. Now, once again, even after Stalin Zanny's experiment, some people still remained skeptical of this idea of biogenesis, that life only comes from life and that life cannot spontaneously generate. Uh they remain skeptical even after Stalin's on his experiment. And so it was not until almost 100 years later, after Stalin's armies experiment that another French scientists of the name Louis pasture was able to confirm stolen Zanny's findings using another simple experiment with a custom flask. And so we'll get to talk about louis Pasteur's experiment uh in our next lesson video. But for now, this year concludes our lesson comparing john Needham's and Lazaro spawns on these experimental design and we'll be able to get some practice applying these concepts as we move forward. So, I'll see you all in our next video