To prepare a wet mount: 1. Add a drop of water or solvent to a clean microscope slide and place the specimen in the liquid. 2. Place a coverslip on the slide so that it touches the edge of the liquid. 3. Slowly lower the coverslip to prevent air bubbles from forming.

2. Preparing a Wet Mount
•
•
•
Using a pipet or dropper, add a drop of water or
another solvent to a clean microscope slide.
Then, place the specimen in the water.
Place the edge of a coverslip on the slide so that
it touches the edge of the water.
Slowly lower the coverslip to prevent the
formation of air bubbles.

4. •
•
•
increases visibility of specimen
accentuates specific morphological features
preserves specimens

5. 
Process by which internal and external
structures are preserved and fixed in
position. Organisms are also killed and
firmly attached to microscope slide.
 heat fixing
▪ preserves overall morphology but not internal
structures
 chemical fixing
▪ protects fine cellular substructure and morphology
of larger, more delicate organisms

6. 
Dyes
 make internal and external structures of cell
more visible by increasing contrast with
background
 have two common features
▪ chromophore groups
▪ chemical groups with conjugated double
bonds
▪ give dye its color
▪ ability to bind cells

7. 
simple staining
 a single staining agent is used
 basic dyes are frequently used
▪ dyes with positive charges
▪ e.g., crystal violet

8. 
divides microorganisms into groups based on
their staining properties
 e.g., Gram stain
 e.g., acid-fast stain

9. 

most widely used differential staining
procedure
divides Bacteria into two groups based on
differences in cell wall structure

10. primary
stain
Gram Stain
Procedure
mordant
decolorization
counterstain
positive
negative

11. Gram stain of Escherichia coli

12. 
Negative staining
 often used to visualize capsules surrounding
bacteria
 capsules are colorless against a stained
background