Hairs & Fibers

Morphology and Structure of Hair

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

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.

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

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 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

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

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.

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.

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.

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.

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.

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 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)

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