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Chapter 11 Hair and Fibers
Forensic Science (CHEM1118)
Fairleigh Dickinson University
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Chapter 11 : Hair and Fibers
Trace Evidence is... ● Evidence occurring in sizes so small that it can be transferred between two surfaces without being noticed ● Examples: ○ Human hair ○ Animal hair ○ Fibers ○ Paint chips ○ Soil ○ Fingernail scrapings ○ Glass fragments Locard Exchange Principle ● Any time there is contact between two surfaces, there will be a mutual exchange or transfer of material ● We're all "Pig Pen" ○ We carry our micro environments with us wherever we go. When our environment comes into contact with another, direct transfer ○ Direct transfer(A to B) ○ Indirect (A to B to C) Hair ● People lose approx 100-200 hairs per day ○ As a result it is a very common type of physical evidence, ● Morphology of hair ○ Hair is an appendage of the skin that grows out of an organ known as the hair follicle ○ Once the hair reaches the skin surface, the cells making them no longer exist. Hair Shaft ● The hair shaft composed of three layers: ○ Cuticle ■ Outside covering of the hair ■ Formed by overlapping scales that always point toward the tip end of each hair ■ The scales of most animal hairs look like shingles on a roof
■ Because scales of animal hair comes in variety of patterns, scale patterns are an important feature for species identification ■ Not useful for individualizing human hair ○ Cortex ■ Located inside the protective layer of the cuticle ■ Made up of spindle-shaped cells that are aligned parallel to the length of the hair ■ Embedded with the pigment granules(melanin) that gives hair its color ■ It is the color, shape, and distribution of these granules that are important for comparison purposes. ○ Medulla ■ The medulla is a collection of cells that look like a central canal that turns through the hair ■ Not at all hairs have a medulla ■ For those hairs that do, the degree of medullation can vary: ● Continuous: Cat hair ● Interrupted: Large pieces, small spaces ● Fragmented: Really broken up ● Absent: No Medulla ■ Human head hairs generally have no medullae or have fragmented ones ■ Most animals will have medullae that are continuous or interrupted ■ The medulla in human hair is not well defined ■ Its diameter relative to the diameter of the hair shaft is less than ⅓ ■ The medulla in an animal hair is well defined ■ Its diameter relative to the diameter of the shaft is ½ or greater** (midterm) Root ● Human head hair goes through three distinct growth phases: ○ Anagen ■ The follicle is actively producing hair ■ The root held tightly in the follicle for continued growth ■ If the hair in this phase was forcibly removed from the head, follicular tissue would adhere to the root sheath
○ Derived entirely from animal or plant sources ○ Animal fibers: wool (Sheep), cashmere (Goat), Fur (Rabbit) ○ Plant fibers: cotton from the flax plant ● Manufactured ○ Derived from either natural or synthetic polymers ○ The first machine-made finer ○ MISSING ● The Cellulose can be chemically treated and dissolved in a solvent, then forced through the small holes of a SPINNING JET TO PRODUCE A PARTICULAR FIBER ● FIBERS MADE FROM NATURAL RAW MATERIAL ARE KNOWN AS REGENERATED FIBERS ● EXAMPLE: Missing ● Synthetic Fibers ○ Fibers produced solely from synthetic chemicals ○ Ex: Nylon, Polyester, Acrylic Laboratory Examination of fibers ● The primary technique used in the ● Microscopic examination. MISSING ○ A comparison microscope- used to identify the color and diameter of the fiber ○ Triacetate vs nylon ● Dye composition ○ Most textile fibers are impregnated with a mixture of dyes to obtain a desirable shade or color ○ When they are viewed under the microscope, there may be differences in the composition of dyes ● Thin layer chromatography (TLC) is a chemical test that is used to separate the dye components ● Sample collection- ○ Fibers are massed produced, making them very common and very abundant ○ Can only give class characteristics ○ Known controls must be collected before a through comparison can be performed
Chapter 11 Hair and Fibers
Course: Forensic Science (CHEM1118)
University: Fairleigh Dickinson University
