When investigators are at the scene of a crime, they look for the smallest pieces of evidence, and then analyze them under a microscope in the lab. Some of the things they might look at are fibers from clothing or carpet, hair, soil tracked in on shoes, fingerprints, and blood stains. Those don’t seem like they’d tell you much, but under a microscope, surprising details come to light.
What You Need:
- Compound microscope
- Plain glass slides
- Paper and #2 pencil
- Several different types of fibers (wool, silk, rayon, etc.)
- Samples of hair from people and animals
What You Do:
Was the criminal wearing a wool sweater or a polyester track suit? You can find out by looking at cloth fibers under a microscope! Wool fibers have very distinctive scales, whereas man-made fibers like nylon or rayon have a very smooth, regular shape.
- Gather samples of several different types of fibers like wool, cotton, rayon, or silk. You don’t have to ruin your shirt to do this! Even just a tiny strand trimmed from the fuzz will work, or look for loose threads. Place your sample on a slide, put a drop of water over it, and cover it with a coverslip.
- Look at the fibers under the microscope and draw pictures to help you distinguish between them. Are they smooth or scaly? Are some thicker than others?
- Have a family member give you a “mystery fiber” and see if you can identify it by comparing it with the samples you prepared yourself.
Hair can also be used for a DNA test if the strand left behind at the crime scene still has the follicle (the part that attaches to the scalp).
- Use the same process to look at a strand of your own hair.
- Try it again with cat or dog hair. Are they scaly too? Do their scales look like human hair, or are they different? Draw the differences.
- Have a family member give you a piece of unidentified hair and see if you can tell whether it is human, cat, or dog.
You learned that by examining the tiny things found in a specifc area ( like a crime scene) under a microscope, you can tell if a human or animal was there and what type of clothing they were wearing. As you study more things under the microscope, you’ll be able to tell if they carried in plant fibers (were they in the garden?) or if they just ate (did they have pizza for lunch?). The more information you gather, the more details you can provide about the crime scene.
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