Text of CHAPTER 10 HAIR AND FIBER. BASIC HAIR STRUCTURE Basic components: keratin (a protein), melanin (a...
CHAPTER 10 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)
Forensic Science Communications January 2004 Volume 6 Number 1 Research and Technology a HAIR STRUCTURE BELOW THE SKIN
HAIR SHAFT Cuticle 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. HumanRat
HAIR SHAFT Medulla 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 INTERRUPTED FRAGMENTED ABSENT
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) MouseFE 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 Human Cow
Absent Medulla No discernable medulla visible Can be found in human hair and animal hair Human Silver fox Human
ANIMAL HAIRS Animal 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, zebra).
HUMAN HAIR 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 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.
Caucasian-Origin Hair Shaft diameter: moderate with minimal variation (mean diameter for human head hairs - 80um) Pigment granules: sparse to moderately dense with fairly even distribution
African-Origin Hair 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
Asian-Origin Hair 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
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
Natural Fibers 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 Cotton fibers Wool Fibers Flax fibers
Synthetic 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
Acetate Luxurious feel, appearance Wide range of colors Shrink, moth & mildew resistant
Aramid Great strength Stretch resistant Does not melt Highly flame-resistant Fibers maintain shape and structure even at very high temperatures
Lyocell Soft, strong absorbent Easily dyed Fiber can be made into many textures
Melamine White fiber, easily dyed Flame resistant Does not conduct heat Plastic used to make unbreakable Dishes Used to make airplane seats Firefighters protective wear
Nylon Early man-made fiber (1930s) Very strong fiber Supple fabric Resilient, holds its shape Abrasion-resistant Lustrous fabric Water-resistant Oil and chemical resistant Used to make seatbelts, clothing, carpets, bedding, drapes, parachutes, tents
Rayon First 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 init