C. Prokaryotic Cells: Use a toothpick to drop some yogurt onto a microscope slide. Cover the sample with a coverslip and observe right away before the yogurt dries out. Two of

the main bacterial types used in making yogurt are Streptococcus thermophilus (chains of spheres) and Lactobacillus bulgaricus (rod- shaped). The bacteria are barely visible using the 40X objective, and most of what you will see on the slide are clumps of casein (milk protein). Starting with the lowest power objective, focus on the casein clumps, then switch to the next highest power objective, and refocus. When you get to 400X total magnification, look for an open space between two thick areas of casein, and look for the tiny bacteria streaming through this space. You might notice the bacteria vibrating a bit as well. It may help to decrease your microscope illumination slightly to see these cells.