In this video, we're going to continue to talk about light microscopes that increase contrast by focusing briefly on phase contrast microscopy. Phase contrast microscopes are microscopes that make cells and their dead structures appear darker than the grayish background that they tend to create. In many phase contrast microscope images, you'll find that the background is going to be a grayish color and the cells and their dead structures will appear darker. However, there are some variations in these phase contrast microscopes that do not necessarily create gray backgrounds. That is not what defines the phase contrast microscopes. Instead, what defines these phase contrast microscopes is the complex special optic devices that they use, which are very complex and beyond the scope of this course. Really, what you can know about these special optic devices is that they increase the differences in how different substances and surroundings refract light differently. Different substances and surroundings refract light differently from each other naturally. However, those differences may be small sometimes. But these special optic devices can increase those differences to make the differences much larger between the two, and ultimately that can help to increase contrast. These phase contrast microscopes can be excellent for enhancing the contrast of internal details in unstained living cells. One of the advantages of the phase contrast microscopes is that there's usually no staining procedure required, and you are able to visualize living cells. Also, phase contrast microscopes can help to reveal cell structures that may not otherwise be able to be visualized using a normal brightfield microscope. These phase contrast microscopes do have advantages. So down below in our example, we're showing you some example images from a phase contrast microscope. With these phase contrast microscopy images, notice that many cases, the backgrounds are going to be grayish, and the cells and the cell structures will tend to appear darker. However, once again, there are some variations in these phase contrast microscopes, and they do not always create gray backgrounds. What classifies all these phase contrast microscopes together is the complex special optic devices that they use. But down below here, what we're showing you is an image from Mucor racemosus mold. Here, we're showing you an image from Cladophialophora bantiana fungus. Here, we're showing you an image of Pleurotus ostreatus fungus spores, and here we're showing you an image of Saccharomyces cerevisiae yeast. Ultimately, what you can take here from phase contrast microscopy is that it is one of the microscopes that's going to help increase contrast and be an alternative use to brightfield microscopes. This here concludes our brief introduction to phase contrast microscopy, and we'll be able to apply some of these concepts as we move forward. So I'll see you in our next video.