Hanging Drop Preparation
A hanging drop preparation is a wet mount method used to observe true motility in living organisms.
Core idea
Motility can support identification branches, but it must be separated from Brownian motion and preparation artifacts.
Principle
A drop of suspension hangs from a coverslip over a depression slide, allowing organisms to move in a thicker fluid space.
Visual reactions
Motility Reading
| Observation | Meaning | Caution |
|---|---|---|
| Directional movement across the field | True motility likely present | Confirm with the organism group and culture condition |
| Vibration in place | Brownian motion | Do not call this motile |
| No movement | Nonmotile or not expressing motility | Temperature, age, and medium can affect expression |
Basic workflow
- Prepare a light organism suspension.
- Place a small drop on a coverslip.
- Invert a depression slide over the coverslip.
- Turn the preparation over carefully.
- Focus on the edge of the drop and observe movement.
How to read it
- True motility shows directional movement through the field.
- Brownian motion appears as vibration without real travel.
- Some organisms require specific conditions to express motility.
High-yield trapCommon mistakes
- Calling Brownian motion motility.
- Using a suspension that is too heavy.
- Letting the mount dry out.
ShortcutStudent shortcut
True motility goes somewhere. Brownian motion just wiggles in place.