In this video, we're going to begin our lesson on John Tyndall's experiment. Now, before we delve into the details of John Tyndall's experiment, it's first helpful to note one of the drawbacks from Louis Pasteur's results were that not every scientist could replicate them when they tried to replicate his experiment. In fact, some scientists who tried to replicate Louis Pasteur's experiment would still discover some microbial growth in the swan-neck flask even after sterilizing with heat. Notice that we have "sterilizing" here in quotes, and that's because these scientists thought that they were sterilizing the flask with heat, when in fact, they were not. But really, it wasn't until John Tyndall came around that people started to realize this fact. John Tyndall was a physicist from the 1800s who showed and explained why sometimes Louis Pasteur's experiment could not always be replicated.
John Tyndall found that some types of broth could not be sterilized even after extremely long boiling times. He realized that depending on the type of broth, it could contain different types of microbes, and he grouped these microbes into two groups: the first group were the heat-sensitive microbes, which are microbes that are sensitive to heat, meaning that these microbes would die when exposed to high enough heat. The second group of microbes that John Tyndall identified were heat-resistant microbes or microbes that are resistant to heat, meaning that they can tolerate and survive in high levels of heat.
If we take a look at this image down below, we can get a better understanding of John Tyndall's experiment, and how he showed why some scientists could not replicate Louis Pasteur's results, and how he further validated biogenesis. Notice over here on the left-hand side, we have an image of John Tyndall who lived from 1820 to 1893 and conducted this experiment in 1881. Notice that here what we have is one of the swan-neck flasks that was used in Louis Pasteur's experiment. Depending on the type of broth, the broth could either contain heat-sensitive microbes, which is what we focus on here at the top, or the broth could contain heat-resistant microbes. Even after really long boiling times, the heat-sensitive microbes, of course, are going to end up as dead cells, as you see here. Because they are sensitive to heat, they will die. That will lead to sterilization. However, the broths that contain heat-resistant microbes, those microbes like it hot, like this guy right here. And because they like it hot, that means that they are going to be resistant and be able to grow and survive because they can tolerate high amounts of heat.
Some of the scientists who tried to replicate Louis Pasteur's experiment were using broth that contained heat-resistant microbes. That's why there was microbial growth in the broth when they thought they were sterilizing when in fact, they were not. The main conclusions of John Tyndall's experiment were that the microbes can exist in two forms: the first form are the heat-sensitive microbes, which are the microbes that die upon exposure to high amounts of heat. But the second type of microbes are the heat-resistant microbes, which can tolerate and survive high amounts of heat. Different types of sterilization techniques will vary for different types of microbes. In order to sterilize the broth that contains heat-resistant microbes, they'll have to use a different type of sterilization technique.
Later in our course, we'll talk all about different types of the scientist Ferdinand Coehn actually discovered what are known as endospores. Endospores are these heat-resistant forms that some bacteria can take on, and we'll talk a lot more about endospores later in our course. But notice that in our image we're showing you these endospores, and these endospores are heat-resistant, and those that's just an example of some heat-resistant microbes. Again, the scientists that had endospore contaminants in their broth would not be able to replicate Louis Pasteur's results. John Tyndall was the one who pointed this fact out, and so this helped to support Louis Pasteur's results and it helped to further validate biogenesis. This here concludes our brief introduction to John Tyndall's experiment, and we'll be able to get some practice applying these concepts as we move forward in our course. So, I'll see you all in our next video.
