Forensic Microscopy Test 3

Hair and Fiber Analysis; Darkfield Microscopy; Phase Contrast Microscopy

Caucasian Hair

Oval cross section, lighter pigmentation, has the most variation

Asian Hair

Evenly dispersed dark pigment, thicker cuticle, round cross section

African Hair

Clumped dark pigment, oblate cross section

Cuticle

Outermost layer, scale pattern

Cortex

Second Layer, Pigment

Medulla

Center/Third Layer, empty

Imbricate Scale Pattern

All humans and some animals

Types of Scale Patterns

Imbricate, Coronal, Spinous

Root Growth Phases

Anagen, Catagen, Telogen

Anagen

Suitable for DNA(capillaries and erector pilli), forcibly pulled out

Catagen

Suitable for DNA,

Telogen

Not suitable for DNA unless follicular tissue is present, inconclusive if hair pulled out forcibly

Coronal Scale Pattern

Crown like pattern

Spinous Scale Pattern

Petal like pattern

Animal v. Human Hair

• Medulla is larger in animals, >1/3 of the total width

• Roots look different

• Animals go from one color to another but humans do not naturally

3 Types of Animal Hair

Tactile, Fur, Guard

Tactile Hair

whiskers

Fur Hair

Fine hair for insulation

Guard Hair

Thick hair for protection, best for forensic examination

Reticle

Piece of glass in the diaphragm of the eyepiece

Calibrating the Reticle

Distance/Reticle Units

Darkfield Microscopy Purpose

black background so the sample appears brighter, only letting non-scattered light through

Darkfield Objectives

Parabloid and Cardiod, do not have lenses but have mirrors: light reflects off of mirrors and comes off on sample at sharp angle

What will the objective say to indicate that it is Darkfield?

Neo, BF/DF, BD or D

How can we increase contrast without DF/PC?

close the aperture diaphragm, change mounting media to something of a different refractive index, stain media

Dark Phase Contrast

Positive contrast, phase shifter is thinner part of the plate and non scattered light goes through phase shifter, causes destructive interference

Bright Phase Contrast

Negative contrast, Phase shifter thicker part of the plate and non scattered light goes through phase shifter, causes constructive interference

What will the objective say for Phase Contrast?

Ph, phase annuli and phase plates have to match

Rheinburg Illumination

optical staining, transparent colored filters for contrast, variation of darkfield

Disadvantage of DF/PC?

Not so good resolution

Phase Contrast Methods

Phase contrast objective lens has phase plate in the diaphragm of the objective lens, ring annulus goes in the condenser

How do we cross section fibers?

1. Pulled pipette taut and cut small section of tube

2. Put fiber in tube

3. Put Norland Optical Adhesive in the end

4. Cure it with UV

5. Take straight razor and cut perpendicular to the fiber, in thin sections

6. Look at the cross section

What are the typical samples for DF/PC?

colorless and thin