Mircoscopy, Hairs and Fibers

Transparent and Translucent Materials:

• Light bends when it passes through objects

• This is due to refractive index

• You will see this in physics

This allows lenses to be produced:

• If the surface is shaped, the light can be focused

• This allows for the creation of lenses

• Function of lenses is dictated by there shape

Devices

• Reading glasses, magnifying glasses have a single lens between the eye and the sample

• Telescopes and Microscopes use combinations of lenses

Light waves are not parallel:

• Coherent light can be oriented in any place around a circle

• But can be polarized

Polarized light:

• When light is polarized, all wavelengths are parallel

• This allows us to exploit refractive index

• Light traveling from one medium to another will all bend in one direction

Becke Lines:

• Bands of light that are seen in a microscope when a sample has a different refractive index than the media it is mounted in

• Significance of the tool

Identification:

• By changing the mounting media, the n of a material can be determined

• This is an identifying physical property

• This is just one use of a microscope

Hair:

• Important as trace evidence

• Resistant to chemical decomposition

• Retains structure for a long period of time

• Remember- class type of evidence unless DNA analysis is completed

• Problems:

  • Misrepresentation of value

  • Contamination

Hair Morphology:

• Outgrowth of the epidermis

• Grows out of hair follicle

• Root/ bulb bottom of follicle, growth here

• Shaft: major portion-extends above surface of skin

• Tip: The terminating end of hair

Morphology:

• Roots: Provides hair with necessary components for growth

  • Nutrients cut off, slowing growth

  • No nutrients, no growth

• Anagen phase: root attached to follicle, can last 6 years

• Catagen phase: Root elongated, growth slows, 2-3 weeks

• Telogen phase: root shrinks and is pushed from follicle

• Cuticle:

  • outer layer of hair

  • Keratinized scales

• Cortexx

  • Second layer, composed of cortical cells or melanocytes

  • Contains the pigments

    • Dark brown

    • Yellow

• Dyed hair

  • Color taken up by the cuticle

    • like paint

    • On the surface only

  • Cortex

    • Melanocytes do no accept dye

• Medulla:

  • Continuous in animals

  • Humans- Presence

    • Continuous

    • Fragmented

    • Interrupted

    • Absent

  • Medullary index: MI=MD/HD

  • Animals MI =/> ½

  • Humans MI < 1/3

• Determination of animal hairs

  • Cuticle cells:

    • Unorganized in humans

    • More patterned in animals

  • Medulla

    • Previously discussed

• Identification and Comparison

  • Match of physical characteristics-class evidence

  • Determination of origin of body area of hair

  • Determination of racial origin of hair

  • Determination of age and sex of origin of hair

  • Determination of forcible removal of hair

  • Individualization of human hair

Testing:

• Comparison Mircoscopy

• Nuclear DNA- individual

• Mitochondrial DNA- traced to maternal side

Collection of Hair Evidence:

• Victim and suspect hairs needed

• Also, elimination hairs needed

• Suitable controls must be present- same body area

• Suitable amount of controls - at least 50 hairs

• Sealed in envelopes is best (other small containers will work)

• Do not remove from larger item

Morphology:

• Fibers and particles have distinct physical charactices

• Hairs for example have visual elements

• Diameter, Scales patterns can help determine species

There are more than 20 characteristics:

• Medullary Index

• Pigment

• Chemical treatment

Fibers:

• Same importance as hairs

• Class evidence, but can have conclusive identification of TYPE of fibers

• Can be easily transferred

• Multiple transfers can take place

• Type of fiber: Natural

• From animals or plant

• Cotton is the most prevalent plant fiber

• Identification through microscopy

• Man made fibers

• Regenerated or semisynthetic

• From Cellulose

• Processed and Reformed

• Man Made fibers- synthetic

• From oil products

• Simple chemicals joined into a very long strand

Polymers:

• Long chains of repeating chemical units

• Homopolymers- one chemical submit

• Copolymers- multiple chemical subunits

• Block Polymers- suitable for fibers

• Crosslinked polymers- used for films

Fiber Morphology

• Type- based on chemical structure

• Cross section

• Color

• Crimp- twist or wave of a fiber

Tear Match (Fracture)

• Conclusive

Analysis of synthetic Fiber:

• Cross section

• Diameter

• Delusterants

• Infrared for chemical composition

• Refractive Index (birefringence)

• Pyrolysis Gas Chromatography

• Color (Metamerism- change of color under different lighting conditions)

Interpretation of results:

• Based on fiber availability

• Dye analysis can help

• Statistics generation