Upload
others
View
7
Download
0
Embed Size (px)
Citation preview
Hairs & Fibers
Morphology and Structure of Hair
Morphology of Hair
An appendage of the skin that grows out of an organ known as the hair follicle.
Extends from its root or bulb embedded in the follicle, continues into a shaft, and terminates at a tip end.
The Shaft of Hair
Composed of three layers: cuticle, cortex, and medulla.
Morphology: Cuticle Protective coating made of
overlapping scales, produce a characteristic pattern
Scales always point toward tip of hair
Not useful in individualizing human hair
Can be used for species identification
http://www.pg.com/science/haircare/hair_twh_35/hair_twh_35_02.jpg
Preserving scale pattern
Since examination of internal structure of hair requires loss of scale pattern, a scale case is made.
Clear nail polish on microscope slide
Hair embedded and allowed to dry before removed.
Differences between animal hairs and human hairs
There are three basic scale structures that make up the cuticle—coronal (crown-like), spinous (petal-like), and imbricate (flattened). Combinations and variations of these types are possible.
http://www.fbi.gov/hq/lab/fsc/backissu/jan2004/research/2004_01_research01b.htm
Differences between animal hairs and human hairs
The coronal, or crown-like scale pattern is found in hairs of very fine diameter and resemble a stack of paper cups. Coronal scales are commonly found in the hairs of small rodents and bats but rarely in human hairs.
http://www.fbi.gov/hq/lab/fsc/backissu/jan2004/research/2004_01_research01b.htm
Differences between animal hairs and human hairs
Spinous or petal-like scales are triangular in shape and protrude from the hair shaft. They are found at the proximal region of mink hairs and on the fur hairs of seals, cats, and some other animals. They are never found in human hairs.
http://www.fbi.gov/hq/lab/fsc/backissu/jan2004/research/2004_01_research01b.htm
Differences between animal hairs and human hairs
The imbricate or flattened scales type consists of overlapping scales with narrow margins. They are commonly found in human hairs and many animal hairs.
Differences between animal hairs and human hairs Human hairs are generally consistent in color
and pigmentation throughout the length of the hair shaft, whereas animal hairs may exhibit radical color changes in a short distance, called banding.
The distribution and density of pigment in animal hairs can also be identifiable features. The pigmentation of human hairs is evenly distributed, or slightly more dense toward the cuticle, whereas the pigmentation of animal hairs is more centrally distributed, although more dense toward the medulla.
The medulla, when present in human hairs, is amorphous in appearance, and the width is generally less than one-third the overall diameter of the hair shaft. The medulla in animal hairs is normally continuous and structured and generally occupies an area of greater than one-third the overall diameter of the hair shaft.
Morphology: Cortex Made of spindle-shaped
cells aligned in a regular array, parallel to the length of the hair
Embedded with pigment granules that give hair its color
The color, shape and distribution of the granules provide points for forensic comparison
www.pg.com/science/haircare/hair_twh_59.htm
Your natural Hair color is determined by three factors
1. The type of natural color pigment
melanin present in your hair's cortex.
Eumelanin (black pigment)
Phenomelanin (red/yellow pigment)
2. How many melanin granules exist
3. Whether those granules are close together or far apart
How Melanin pigments determine your natural haircolor:
Black hair contains densely packed melanin granules full of
eumelanin. Brown hair has a loose pattern of eumelanin-filled
granules or granules blended with eumelanin and phenomelanin, depending upon its cool or warm tones and its darkness or lightness.
Blonde hair contains few granules with minimal bits of
eumelanin. In fact, the eumelanin is so sparse that the color of blonde hair is the color of the hair fiber itself.
Red hair has loosely packed granules containing
phenomelanin.
What causes gray hair? As you age, your natural production of
pigment slows down and your natural color loses its color strength.
This doesn't happen to every hair at the same time, so the contrast between the hair with no color and the hair that still has some color causes it to look gray.
So how gray your hair actually looks is determined by the percentage of strands with no color vs. the pigmented strands.
Morphology: Medulla
canal like structure of cells that runs through the center of the cortex
Medullary Index
Measure of the diameter of the medulla relative to the diameter of the hair shaft
Usually expressed as a fraction
Humans: medullary index < 1/3
Animals: medullary index > 1/2
Medullae of Different Species
Medulla Shape Medulla shape is another characteristic
that varies from species to species
UNISERIAL (rabbit)
MULTISERIAL (rabbit)
VACUOLATED (dog, fox,
common)
LATTICE (deer)
AMORPHOUS (human,
common) 20
Medulla of Different Species
Forensic Analysis of Medulla Presence of medulla varies quite a bit: even hair
to hair Human head hairs generally have no medulla or
may be fragmented ones; except Mongoloid (Asian) race whose medulla is usually continuous
Most animals have medulla that is continuous or interrupted
The shape of the medulla can help identify a species
Examples: Most animals and humans: cylindrical Cats: pearl shape Deer: spherical occupying whole hair shaft
Comparison of Animal and Human Hair
Medullary Index ≥1/2
Medulla is present for all animals
Medulla is continuous for most animals
Medulla is patterned for most animals
Medullary Index <1/3
Medulla is absent for most humans
Medulla is continuous for Mongoloid race
Medulla is fragmented – only some animals and humans
Medulla is cylindrical in shape (most animals)
Identification and Comparison of Hair
Morphological Characteristics do not allow individualization of a human hair to any single head or body
Hair when collected with an adequate number of standards/references can provide strong circumstantial evidence
Scale structure, medullary index, and medullary shape are most often used for hair comparison
Evidential value lies with degree of probability associated with a questioned hair and an particular individual
11 percent of all morphological hair matches are generally found to be non-matches—meaning microscopic hair comparisons are presumptive in nature—must be confirmed by DNA comparisons
Human Hairs
Racial Determination
Body Area
Age and Sex?
Forcibly Removed?
Can the racial origin of hair be determined?
Forensic terms: Caucasoid, Negroid, Mongoloid
Mongoloid has continuous medullae
Caucasian has even distribution of pigment in cortex
Negroid has unevenly distributed pigment.
http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric1.htm
Racial Determination
Negroid
Mongoloid
Caucasoid
Usually kinky, containing dense, unevenly distributed pigments.
Cross section is flat to oval in shape.
Usually straight or wavy with very fine to coarse pigments that are more evenly distributed .
Cross section are oval to round in shape.
Usually coarse containing pigment granules larger in size than Caucasians.
Cross sections are round in shape.
Head Hairs
Long with moderate shaft diameter and diameter variation
Medulla absent to continuous and relatively narrow when compared to the structure of hairs from other body areas
Often with cut or split tips
Can show artificial treatment, solar bleaching, or mechanical damage
Soft texture, pliable
Pubic Hairs
Medulla relatively
broad and usually
continuous when
present
Root frequently
with tag
Tip usually tapered, rounded, or
abraded
Stiff texture, wiry
Shaft diameter
coarse with
wide
variations and
buckling
Limb Hairs
Tips usually tapered, often blunt and abraded, rounded scale ends due to wear
Diameter fine with little variation Gross appearance of hair is arc-like in shape
Medulla is discontinuous to trace with a granular appearance
Soft texture
Facial Hairs (Beard/Mustache)
Diameter very coarse with irregular or triangular cross-sectional shape
Medulla very broad and continuous, may be doubled
Chest Hairs
Shaft diameter moderate and variable
Tip often darker in color, long and fine, arc-like
Medulla may be granular
Stiff texture
Axillary or Underarm Hairs
Resemble pubic hairs in general appearance, but less wiry
Medullary appearance similar to limb hairs
Diameter moderate and variable with less buckling than pubic hairs
Tips long and fine, frequently with bleached appearance
Other Body Hairs
Eyebrow: Stubby, some diameter fluctuation, saber-like in appearance
Eyelash: Short, stubby with little shaft diameter fluctuation, saber-like in appearance
Trunk: A combination of features of limb and pubic hairs, a transitional hair
Tip of the Shaft
Burned Cut Razored Split
Root of Hair
Provide the tools to produce hair and continue its growth
3 Stages of Growth (different looking roots) Anagen -initial phase may last up to 6 years, root is
flame shaped Catagen –transition phase (2-3 weeks), root is
elongated Telogen –phase where hair naturally falls out of the
skin, root is club-shaped
Hair Growth Cycle
Forcibly Removed?
Pulled Forcibly Removed Shed
A normal telogen hair with a
hard 'club' end, seen under
(left) a light microscope and
(right) an electron microscope
An anagen hair that has been
plucked out: notice the soft,
sticky tail
Brushed-out hairs all have
this kind of root.
This is an anagen hair,
one which was pulled
out and not ready to be
shed.
Collection of Hair Evidence
Collection of Hair Evidence
Questioned and Reference hair must come from same area of the body; one cannot, for instance compare head hair to pubic hair.
The collection of 50 full length hairs from all areas of the scalp will normally ensure a representative sampling of head hair.
Collection of Hair Evidence
A minimum collection of 24 full length pubic hairs should cover the range of characteristics present in this type of hair.
All collected hairs must be full-length so that the investigator can see if the color and morphological features vary throughout the length of the hair.
Packaging of Hair Evidence
Recover all hair present. If possible, use fingers or tweezers to pick up
hair, place in paper bindles or coin envelopes which should then be folded and sealed in larger envelopes.
Label the outer sealed envelope. If hair is attached, such as in dry blood, or
caught in metal or a crack of glass, do not attempt to remove it but rather leave hair intact on the object.
If the object is small, mark it, wrap it, and seal it in an envelope.
If the object is large, wrap the area containing the hair in paper to prevent loss of hairs during shipment
Fibers: Natural Derived entirely from animal or
plant sources
Most prevalent plant fiber is cotton.
Its widespread use has made its evidential value almost meaningless
Cotton has a ribbon-like shape with twists at regular intervals
Animal sources include sheep (wool), goats (mohair, cashmere) and many other sources
http://www.swicofil.com/images/cotton_microscopic.jpg http://www.e4s.org.uk/textilesonline/content/6library/report1/images/microscope_2.gif
Wool
Cotton
Man-Made Fibers
Fibers derived from either natural or synthetic polymers
The fibers are made by forcing polymeric material through the holes of a spinneret
Rayon and then nylon were the first two man-made fibers (year 1911)
http://www.naturalvisions.co.uk/pictures/thumbnail/XMIC_0021_0001XX.jpg
Man-Made Fibers Con’t Regenerated Fibers
Made from regenerated cellulose (wood or cotton pulp)
Include such fibers as rayon, acetate, and triacetate
Synthetic Fibers Currently manufactured
Made from synthetic chemicals called polymers
Include such fibers as nylons, polyesters, and acrylics
ID and Comparison of Man-Made Fibers
Fabrics that can be fitted together at their torn edge are easy to match
Microscopic comparison of color and diameter
Comparison of lengthwise striations and pitting on the surface of a fiber
The shape of the fiber—ex. Wayne Williams case Cross sections are generally helpful
Note: Combined factors of color, size, shape, microscopic appearance, chemical composition, and dye content make it very unlikely to find two different people wearing identical fabrics
ID and Comparison of Man-Made Fibers con’t.
The chemical makeup of the fiber itself can be examined through the following:
Infrared microspectrophotometry
Refractive Index
The chemical makeup of the dyes in the fiber can be examined through the following:
Liquid chromatography
Visible light microspectrophotometry