1. Locard’s Exchange Principle

2. Locard’s Exchange Principle
The value of trace (or contact) forensic evidence was first recognized by Edmund Locard in He was the director of the very first crime laboratory in existence, located in Lyon, France.
Locard’s Exchange Principle states that “with contact between two items, there will be an exchange.” In other words: “Every contact leaves a trace!”

3. Examples of Things that can be Transferred:
Paint
Fracture Matches when an object is broken
Glass
The shape and depth of a wound
Traces of Chemicals used in Explosives
Documents
Characteristics of ammunition, firearms, and chemical residue
Insects
DNA
Dust and Dirt Particles
Body Fluids
Fingerprints
Hair and Fibers
Impression Evidence: shoe prints, tire tracks, bite marks, tool marks

4. Microscope Review

5. Microscope Parts Eyepiece Body Tube Revolving Nosepiece Arm
Objective Lens
Stage
Stage Clips
Coarse Focus
Fine Focus
Base
Diaphragm
Light
This is the microscope used in class. Students will be identifying the parts on the microscopes at their desks as we go along and what their functions are.

6. Using the Microscope
General Procedures
1. Make sure all backpacks and materials are out of the aisles and off the tops of desks. 
2. Plug your microscope in to the outlet.
3. Store with cord wrapped around microscope and the scanning objective clicked into place.
4. Carry by the base and arm with both hands.

7. Magnification
Your microscope has 3 magnifications: Scanning, Low and High. Each objective will have written the magnification. In addition to this, the ocular lens (eyepiece) has a magnification. The total magnification is the ocular x objective

8. Focusing Specimens DO NOT SKIP STEPS!!!!
1. Always start on the Lowest Power (scanning lens). Move the slide around until you see something in the lens. Use the Coarse Adjustment Knob to refocus. Then use the Fine Adjustment Knob to make the image crystal clear. If you don’t focus on this level, you will not be able to move to the next level. 2. Now switch to a Higher Power. (If you have a thick slide, or a slide without a cover, do NOT use the high power objective). At this point, ONLY use the Fine Adjustment Knob to focus specimens. Recap 1. Low power --> use coarse and fine knob 2. High power --> use fine knob only
DO NOT SKIP STEPS!!!!

9. Troubleshooting
Occasionally you may have trouble with working your microscope. Here are some common problems and solutions. 1. Image is too dark! Adjust the diaphragm, make sure your light is on. 2. There's a spot in my viewing field, even when I move the slide the spot stays in the same place! Your lens is dirty. Use lens paper, and only lens paper to carefully clean the objective and ocular lens. The ocular lens can be removed to clean the inside. The spot is probably a spec of dust. 3. I can't see anything under high power! Remember the steps, if you can't focus under scanning and then low power, you won't be able to focus anything under high power. Start at scanning and walk through the steps again. 4. Only half of my viewing field is lit, it looks like there's a half-moon in there! You probably don't have your objective fully clicked into place..

10. How to Create a Wet Mount Slide
Using a pipet or dropper, add a drop of water to a clean microscope slide.
Place your specimen in the water.
Hold the coverslip at a perpendicular angle to the slide.
Place the edge of the coverslip on the slide so that it touches the edge of the water.
Slowly lower the coverslip to prevent the formation of air bubbles.