chapter 10 hair and fiber. basic hair structure basic components: keratin (a protein), melanin (a...
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HAIR AND FIBER
BASIC HAIR STRUCTURE• Basic components:
keratin (a protein), melanin (a pigment), and trace quantities of metallic elements (Cu, Fe, Mn,etc).
• Elements are deposited in hair during growth and absorbed by the hair from external environment.
More on Hair Basics• All 5 million hair follicles are
formed by week 22 during fetal development.
• 100,000 follicles on the scalp.
• You have the most follicles when you are born – as body size decreases with age so does the number of hair follicles – NEVER get any new ones
• Hair is found on all visible body surfaces.
• Hair is the only structure that is completely renewable without scarring
• Hair goes about 0.5 inch per month (~ 6 inches per year)
HAIR STRUCTURE BELOW THE SKIN
HAIR SHAFTCuticle – First Layer
• The cuticle is a translucent outer layer of the hair shaft consisting of scales that cover the shaft.
• The cuticle scales always point AWAY from the root end - toward the tip of the hair.
CUTICLE SCALES: CORONATE
• Scales show crown- shaped pattern
• Found in small rodents and bats
• Coronate pattern NEVER seen in human hair
FREE-TAILED BAT HAIR
CUTICLE SCALES: SPINOUS• Spinous - petal-like
scales are triangular in shape and protrude from the hair shaft.
• Spinous are found close to the body on mink, and on seals, sea lions, fox and cats
• Never found in humans.
CUTICLE SCALES: IMBRICATE• The imbricate (brick-
like) or flattened scales. Consists of tightly overlapping scales with narrow margins between the scales.
• Usually only found in human hair (some animal species).
HAIR SHAFT Cortex – Second Layer
• The area between the cuticle and the core of the hair.
• Contains all the pigment granules, ovoid bodies and any moisture
PIGMENT GRANULES• Pigment granules are small, dark, and solid structures
that look like grains of sand • They contain melanin• In humans, pigment granules are found in the cortex
closest to the cuticle• Animal hairs have pigment granules only in the medulla.
HAIR SHAFTMedulla – Center Layer
• The medulla is a central core of cells that may be present in the hair.
• Human hair - the medulla unorganized, random pattern
• Animal hair - structure is well defined
• Some medullary patterns:
Continuous Medulla• Medulla has solid
continuous medulla through the entire hair shaft.
• No breaks or gaps
Upper - human hair Lower - lattice pattern of a deer
Medulla - Interrupted• Pattern is repeated over and over in the hair
shaft at regular intervals. • Common in rodent hair (rats, mice, guinea
pigs, ferrets, bats)Guinea Pig
Multiserial ladder (rabbit)
Mouse FE Ferret
FRAGMENTED• Bubbly or cellular medullary area• Center of hair shaft appears hollow with bubble or cell-like
pattern but can have a few parts visible• Most common in human hair but can be found in animals
Absent Medulla• No discernable
• Can be found in human hair and animal hair
ANIMAL HAIRSAnimal hair always has a medullary index of 1/3 or greater.Animal roots are usually rounded in shape.Animal hairs are classified into the following four basic types.• Guard hairs that form the outer coat of an animal and provide protection • Fur or wool hairs that form the inner coat of an animal and provide
insulation • Tactile hairs (whiskers) located on the head provide sensory functions • Types of hairs found on animals include tail hair and mane hair (horse,
• The root is club-shaped • Consistent in color and
pigmentation throughout the length of the hair
• Medullary index is less than 1/3
• Pigment is evenly distributed, slightly more dense near the cuticle
Pigment Distribution in Human Hair
• Pigment granules are small, dark, and solid structures
• They vary in color, size, and distribution in a single hair.
• In humans, pigment granules are commonly distributed toward the outer edge of cortex
• The exception is red-haired individuals, granules are concentrated along the center of the hair
Brown Human Hair
Red Human Hair
• Scale casts may also be prepared using clear nail polish.
• A thin coat is painted on a glass microscope slide or, if the lacquer is thinned with acetone, a drop may be allowed to run down the surface of the slide.
• The hair is placed on the slide and allowed to dry.
• When the surface has dried, the hair is removed to reveal the scale pattern.
Scale Cast of Human Hair
Microscope Slide Preparation
• Positioning a hair on the glass slide by first applying a thin film of nail polish on the slide surface.
• Longer hairs are placed in a figure eight in order to fit it under the cover slip. This enables the examiner to view the entire hair from root to tip.
• Several drops of mounting medium are applied on top of the hair
• A cover slip is carefully lowered to prevent the presence of air bubbles.
• It may be necessary to apply some weight to the cover slip in order to ensure a thin mount.
Human HairsHuman Hairs
Racial DeterminationRacial Determination
Negroid Mongoloid Caucasian
• Shaft diameter: moderate with minimal variation (mean diameter for human head hairs - 80um)
• Pigment granules: sparse to moderately dense with fairly even distribution
• Shaft diameter: moderate to fine with considerable variation
• Pigment granules: densely distributed (hair shaft may be opaque) and arranged in prominent clumps
• Shaft: prominent twist and curl
• Shaft diameter: coarse and usually with little or no variation
• Pigment granules: densely distributed and often arranged in large patchy areas or streaks
• Medulla: prominent (often broad and continuous)
• Cuticle: thick
Hair RootsHair Roots
Pulled Forcibly Removed Shed
Tip of the ShaftTip of the Shaft
Burned Cut Razored Split
Types of Fibers• Natural fibers are derived in whole from animal or
plant sources.– Examples: wool, mohair, cashmere, furs, and cotton.
• Man-made fibers are manufactured.– Regenerated fibers are manufactured from natural raw
materials and include rayon, acetate, and triacetate.– Synthetic fibers are produced solely from synthetic
chemicals and include nylons, polyesters, and acrylics.
• Polymers, or macromolecules, are synthetic fibers composed of a large number of atoms arranged in repeating units known as monomers
• Fibers that are from plant or animal sources
• Cotton fibers are the most common plant fibers
• Other plant fibers used in the production of textiles include flax (linen), ramie, sisal, jute, hemp, kapok, and coir
• The most common animal fiber is wool that is taken from sheep.
• Woolen fibers from other animals include camel, alpaca, cashmere, mohair
Wool Fibers Flax fibers
• More than half of all fibers used in the production of textile materials are man-made.
• Polyester and nylon fibers are the most commonly encountered man-made fibers, followed by acrylics, rayons, and acetates.
• The shape of a man-made fiber can determine the value placed on that fiber.
• The cross section of a man-made fiber can be manufacturer-specific
AcetateLuxurious feel, appearanceWide range of colorsShrink, moth & mildew resistant
AcrylicSoft, warmWool-likeFiber retains shapeResilientQuick-dryingShrink, moth, fade resistant
AramidGreat strengthStretch resistantDoes not meltHighly flame-resistantFibers maintain shape and structure even at very high temperatures
LyocellSoft, strong absorbentEasily dyedFiber can be made into many textures
White fiber, easily dyedFlame resistantDoes not conduct heatPlastic used to make “unbreakable” DishesUsed to make airplane seatsFirefighter’s protective wear
Early man-made fiber (1930’s)Very strong fiberSupple fabricResilient, holds it’s shapeAbrasion-resistantLustrous fabricWater-resistant Oil and chemical resistantUsed to make seatbelts, clothing, carpets, bedding, drapes, parachutes, tents
RayonFirst manufactured in 1911
Fiber Evidence• The quality of the fiber evidence depends
on the ability of the criminalist to identify the origin of the fiber or at least be able to narrow the possibilities to a limited number of sources.
• Obviously, if the examiner is presented with fabrics that can be exactly fitted together at their torn edges, it is a virtual certainty that the fabrics were of common origin.
Fiber Evidence• Microscopic comparisons between questioned and
standard/reference fibers are initially undertaken for color and diameter characteristics, using a comparison microscope.
• Other structural features that could be important in comparing fibers are: – Lengthwise striations on the surface of the fiber.– The presence of delustering particles that reduce shine.– The cross-sectional shape of the fiber.
• Compositional differences may exist in the dyes that were applied to the fibers during the manufacturing process.
Fiber Analysis• The visible light microspectrophotometer is a
convenient way for analysts to compare the colors of fibers through spectral patterns.
• A more detailed analysis of the fiber’s dye composition can be obtained through a chromatographic separation.
• Infrared spectrophotometry is a rapid and reliable method for identifying the generic class of fibers, as does the polarizing microscope.
• Depending on the class of fiber, each polarized plane of light will have a characteristic index of refraction.
Evidence Collection• The investigator’s task of looking for
minute strands of fibers often becomes one of identifying and preserving potential “carriers” of fiber evidence.
• Relevant articles of clothing should be packaged carefully in separate paper bags.
• If it is necessary to remove a fiber from an object, the investigator must use clean forceps, place it in a small sheet of paper, fold and label the paper, and place the paper packet inside another container.