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Chapter 10 Trace Evidence: Hairs and Fibers

Chapter 10 Trace Evidence: Hairs and Fibers. Objectives: Describe the cuticle, cortex, and medulla of hair. Describe the three phases of hair growth. Explain the distinction between animal and human hairs. List hair features that are useful for the microscopic comparison of human hairs.

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Chapter 10 Trace Evidence: Hairs and Fibers

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  1. Chapter 10Trace Evidence: Hairs and Fibers Objectives: Describe the cuticle, cortex, and medulla of hair. Describe the three phases of hair growth. Explain the distinction between animal and human hairs. List hair features that are useful for the microscopic comparison of human hairs. Explain the proper collection of hair evidence. Describe the role of DNA typing in hair comparisons. Created by C. Ippolito April 2008

  2. Morphology of Hair • skin appendage • hair follicle • cuticle • cortex • medulla Created by C. Ippolito April 2008

  3. Cuticle • outer covering • overlapping scales • keratinized cells • distinguish human from animal • cast in enamel/vinyl • scale patterns used to identify Created by C. Ippolito April 2008

  4. Medulla • central canal • narrow in human • wide in animals • patterns used to id animals • Sample Animal Hairs multiserial ladder uniserial ladder vacuole lattice fragmented continuous Created by C. Ippolito April 2008 interrupted

  5. Cortex • between cuticle and medulla • contains pigment • color shape distribution • contains fusi (air pockets) Created by C. Ippolito April 2008

  6. Growth Stages • root • anagen (lasts 6 years) • active growing follicle makes hair • follicular tag • rich in DNA • catagen (2-3 weeks) • root elongated • transition phase • telogen (2-6 months) • root club shaped • shaft pushed out (shed) Created by C. Ippolito April 2008

  7. root bulbous banding artificial dyes medulla narrow root varies spade (dog) frayed (cat) wine glass (deer) natural banding medulla wide Human/Animal Hair Comparison Created by C. Ippolito April 2008

  8. Caucasian dia: moderate pig: sparse -moderately dense XS: oval Negroid fine–moderate dense & clumped flattened Human Race Comparison • Asian • coarse • dense-patches • round w/thick cuticle Created by C. Ippolito April 2008

  9. Human Hair Color Comparison • based on pigment distribution Created by C. Ippolito April 2008

  10. head – straight shaft pubic – “twists” in shaft Head/Pubic Hair Comparison Created by C. Ippolito April 2008

  11. FBI Hair Comparison Paper • Scientific Paper Created by C. Ippolito April 2008

  12. Chapter 10Trace Evidence: Hairs and Fibers Objectives: Classify fibers. Describe the structure of a polymer. List the properties of fibers that are most useful for forensic comparisons. Describe the proper collection of fiber evidence. Created by C. Ippolito April 2008

  13. Fiber Evidence • Is the second most common type of trace evidence Created by C. Ippolito April 2008

  14. Fiber Evidence Classifications Created by C. Ippolito April 2008

  15. Natural Fiber Classifications • Learn more details about the types of fibers at the following link http://www.teonline.com/fiber-history.html Created by C. Ippolito April 2008

  16. Mineral Fibers • Asbestos • Insulation • Fire retardant • Fiberglass • Filters • Insulation Created by C. Ippolito April 2008

  17. Plant Fibers • Cotton • Too common • Little significance • Kapok • Flotation devices • Very buoyant • Flax • Linen • Bamboo shaft like • Hemp • Large diameter • Cords and ropes Created by C. Ippolito April 2008

  18. Animal Fibers • Wool • Sheep hair • Coarse, irregular • Cashmere • Goat hair • Smooth • Camel • Fine diameter • Silk • Secretion of insect • Small diameter Created by C. Ippolito April 2008

  19. Manufactured Fiber Classifications Created by C. Ippolito April 2008

  20. Regenerated Manufactured Fibers • Acetate (Celanese) • Cellulose acetate • luxurious • soft • fast drying • shrink, moth, mildew resistant • Rayon • Cellulose fibers • highly absorbent • soft • easily dyed • Triacetate • shrink, wrinkle resistant • washable • maintains creases and pleats well Created by C. Ippolito April 2008

  21. Synthetic Manufactured Fibers • Acrylic • fluoresce in UV • warm • wool like • moth, oil, chemical, sunlight resistant • Aramid (Kelvar) • heat resistant strong fibers • does not melt (500°C) • flame, stretch resistant • strength for weight Created by C. Ippolito April 2008

  22. Synthetic Manufactured Fibers (con’t.) • Nylon • polyamide (peptide bonds) • strong • lustrous • washable • resilient • Olefin • polypropylene, polyethylene • wicks moisture • quick drying • soil, mildew, perspiration, rot, weather resistant • strong/lightweight Created by C. Ippolito April 2008

  23. Synthetic Manufactured Fibers (con’t.) • Polyester • Dacron (ester bonds) • strong • stretch, shrink, chemical, wrinkle resistant • retains heat set pleats/creases • washable • quick drying • Spandex • Polyether polyols • can stretch 500% without breaking • returns to original shape • light weight • stronger than rubber • resistant to body oils Created by C. Ippolito April 2008

  24. Fiber Identification and Comparison • Microscopic Examination • striations, pitting may be characteristic of fibers • cross section shape • Chemical Composition • textile chemists have test to help classify polymer types • Birefringence (refractive indices) • polymers are crystalline – see table p 376 • Infrared Absorption • absorption spectra can be used to identify generic class of fiber Created by C. Ippolito April 2008

  25. Collection and Preservation of Fiber Evidence • most fiber evidence not visible to naked eye • need to preserve “carriers” of fiber evidence • carefully package clothing in paper bags • don’t package from same surface • fold to protect suspected areas Created by C. Ippolito April 2008

  26. References • Houck, Max M. “Forensic Hair Comparisons.” Forensic Business Research and Development for College of Business and Economics of West Virginia University Created by C. Ippolito April 2008

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