Test 4 - Fiber, Hair Analysis

Crimes Involving Fiber Evidence

• Homicide

• Battery

• Sexual battery

• Hit and run

• Burglary

Natural Fibers

Derived from animal (hair/fur) or plant

• Classified according to their origin

  • Vegetable or cellulose-based

    • Cotton, jute, hemp

  • Animal or protein-based

    • Wool, mohair, silk

  • Mineral class

    • Asbestos

Cotton

• Grow on thorny plants and have sticky seeds

• Ribbon-like with twists

• Hollow

Silk

• Made from silkworm cocoons

• Fibers are:

  • Smooth

  • Naturally transparent

Wool

• Appears round

• Cuticle pattern

  • Scale-like markings

Goat Hair Fibers

• Mohair

• Cashmere

Man-made Fibers

fibers derived from natural or man-made polymers

Polymer

• A combination of many subunits

• A substance composed of a large number of atoms (macromolecules) arranged in repeating units of monomers

• Monomer - basic unit of a polymer

Regenerated Fibers

• Man-made but from natural sources (cotton or wood pulp to get cellulose)

Rayon

First regenerated fiber

Fiber Analysis (Hard)

• Single fibers

• Microscopic Comparative Studies

1. Color comparison

2. Diameter comparisons

3. Examination for lengthwise striations

4. Examination for pitting

5. Look at cross-sectional shape

Striations

banding/grooves going lengthwise on fibers

Color Analysis of Fibers

• Compare dyes of two different fibers

• Use Thin-layer Chromatography

Thin-layer Chromatography

chemical analysis of dyes in a fiber

Layers of Shaft (moving inward)

• Cuticle

• Cortex

• Medulla

Cuticle Layer

• Tough and resistant outer layer

• Formed by overlapping scales

  • Point toward the tip of the hair

  • Specialized keratinized cells (hardened)

  • Flattened in progressing from the follicle

• Used for species identification

  • Coronal - mouse

  • Spinous - cat

  • Imbricate - human

    • very irregular pattern

Casting

• Use clear nail polish to create an impression of the cuticle pattern on a microscope slide

• Observe under a microscope

Cortex Region

• Beneath the cuticle

• Composed of spindle-shaped cells aligned parallel to the length of the hair

• Embedded with pigment granules

• Look at color, shape, and distribution of granules

Medulla Region

• Center region of hair

• Presence and pattern varies from person to person and from hair to hair on an individual

  • Fragmented - Short, discontinuous section

  • Intermittent - long, discontinuous sections

  • Continuous - one long section

Follicular Tissue

Skin cells from the hair follicle that are on the end of the hair when forcibly pulled

Anagen

• actively growing

• root is flame-shaped

Catagen

• slowed growth

• root elongated and shrunken

Telogen

• hair growth ends

• root is club-shaped

• hair falls out of cuticle

Hair: Comparative Studies

• Dyed hair (paint roller) vs. Natural

• Bleached hair (yellowish tint)

• Time of dyeing (hair grows 1cm/month)

• Nits or fungal infections

Hair Growth Rate

1 cm/month

Types of Hair

• Scalp = uniform diameter and pigment distribution

• Pubic = short, curly and diameter variations

• Facial = coarse, triangular, blunt tips

Baby Hair

Age cannot be determined by hair, unless it is the very distinct baby hair

Drug Use

drugs and poisons will remain in the hair

• you can tell when a person used a drug, such as marijuana and cocaine, based on where it is on the hair