Hairs

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Hairs Fibers
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Morphology and Structure of Hair
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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/hai
r_twh_35_02.jpg
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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
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Morphology Medulla

• canal like structure of cells that runs through
  the center of the cortex (pg. 53)

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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 lt 1/3
• Animals medullary index gt 1/2

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Medullae of Different Species
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Medulla of Different Species
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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

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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-matchesmeaning
  microscopic hair comparisons are presumptive in
  naturemust be confirmed by DNA comparisons

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Can the racial origin of hair be determined?

• Forensic terms Caucasian, Negroid, Mongoloid
• Mongoloid has continuous medullae
• Caucasian has even distribution of pigment in
  cortex
• Negroid has unevenly distributed pigment.

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Hair from different parts of the body

• Scientists distinguish 6 types of hair on the
  human body head hair, eyebrows/eyelashes/
  beard/mustache, underarm, body hair, and pubic
  hair
• Eye hairs are usually saber-like and stubby
• Facial hairs have a coarse diameter and the
  medulla may be doubled
• Underarm hairs resemble pubic hairs, but are less
  wiry
• Pubic hairs have a coarse diameter, buckling is
  present, and the medulla is continuous (when
  present)

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Beard, arm, and pubic hairs
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Differences between animal hairs and human hairs

• There are three basic scale structures that make
  up the cuticlecoronal (crown-like), spinous
  (petal-like), and imbricate (flattened).
  Combinations and variations of these types are
  possible.

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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.

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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/res
earch/2004_01_research01b.htm
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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.

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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.

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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

Cotton
Wool
http//www.swicofil.com/images/cotton_microscopic.
jpg
http//www.e4s.org.uk/textilesonline/content/6libr
ary/report1/images/microscope_2.gif
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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
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Man-Made Fibers Cont

• 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

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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 fiberex. 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