Chapter 3 The Study of Hair

Transcription

1 Chapter 3 The Study f Hair Vcabulary: Class evidence: Cmparisn micrscpe: a cmpund micrscpe that allws the side-by-side cmparisn f samples, such as f hair r fibers Crtex: Cuticle: Hair fllicle: the actively grwing rt r base f a hair cntaining DNA and living cells Individual evidence: Keratin: a type f fibrus prtein that makes up the majrity f the crtex f a hair Medulla: Melanin granules: Neutrn activatin analysis: a methd f analysis that determines cmpsitin f elements in a sample Trace evidence: small but measurable amunts f physical r bilgical material fund at a crime scene By the end f this chapter yu will be able t: identify the varius parts f a hair describe variatins in the structure f the medulla, crtex, and cuticle distinguish between human and nnhuman hair determine if tw examples f hair are likely t be frm the same persn explain hw hair can be used in a frensic investigatin calculate the medullary index fr a hair 1

2 Histry f Hair Analysis Alfred Swaine Taylr and Thmas Stevensn, in 1883, wrte a frensic science text that included a chapter n hair. Victr Balthazard and Marcelle Lambert, in 1910, published a cmprehensive study f hair. Dr. Sydney Smith, in 1934, first used a cmparisn micrscpe t analysis hairs side by side. Advances cntinue tday with chemical tests, neutrn activatin analysis, and DNA analysis. The Functin and Structure f Hair Hair n mammals helps t Hair cnsists f (a) (b) A hair has three layers: Types f Cuticle and Crtex The Cuticle is the utermst layer made f ver-lapping scales that prtect the inner layers f the hair. The Crtex is the thickest layer cntaining mst f the pigment giving hair its clr. The distributin f pigment in the crtex 2

3 Types f Medulla The medulla (the inner sectin) can be 3

4 Types f Hair 3 types: The crss sectin f a hair can be Crss sectin influences the curl f the hair The texture f a hair can be Different regins f the bdy n which hair can vary are (1) (2) (3) (4) (5) (6) 4

5 The Life Cycle f Hair Hair prceeds thrugh 3 stages as it develps: hair actively grws cells arund the fllicle rapidly divide depsit materials in the hair hair grws and changes fllicle becmes drmant hairs easily can be lst Treated Hair Frensic investigatrs smetimes can link hair frm a lcatin with an individual Bleaching disturbs the scales n the cuticle and remves pigment leaving hair brittle and a yellwish clr Because f this and because hair grws daily, a persn s treated hairs will have specific characteristics in cmmn with her r his lst hairs Racial Differences Hair examiners have identified sme physical characteristics that generally can be assciated with brad, racial grups. These characteristics, hwever, will nt apply t all individuals in these grups. In additin, at times, it will be impssible t assign specific hairs t any f these grups be-cause their characteristics are prly defined r hard t measure. 5

6 Animal Hair and Human Hair Cre: Thickest layer: Outermst: Pigmentatin in animal hair In Humans it tends t be denser tward the cuticle. Unlike human hair, animal hair abruptly can change clrs in banded patterns. The medullary index is different in Spinus Crnal Imbricate The utermst layer f the hair shaft (the cuticle), is typically different in animals and humans. The cuticle scales in animals tend t resemble r give the appearance f a The cuticle scales in humans cmmnly are Using Hair in an Investigatin Macrscpic investigatin can indicate 6

7 Micrscpic investigatin can indicate fine detail in hair structure. Phase cntrast micrscpy, fr example, can shw the presence f dye r ther treatments. Electrn micrscpes can prvide mre detail f the surface r interir f the sample. In the sample abve, nte the verlapping scales and the pigment granules in the crtex. Testing fr Substances in the Hair Shaft Chemicals that the skin absrbs ften can be detected by analysis f the hair shaft. The hair shaft can be examined in sectins t establish a timeline fr expsure t txins. Neutrn Activatin Analysis (NAA) can determine Testing the Hair Fllicle Micrscpic assessment f the fllicle is perfrmed first because it is cst effective and quick. If a micrscpic match is fund Chapter 4 A Study f Fibers and Textiles Vcabulary: Amrphus: withut a defined shape; fibers cmpsed f a lse arrangement f plymers that are sft, elastic, and absrbing (fr example, cttn) Crystalline: regularly shaped; fibers cmpsed f plymers packed side by side, which make it stiff and strng (fr example, flax) Direct transfer: 7

8 Fiber: Mineral fiber: a cllectin f mineral crystals frmed int a recgnizable pattern Mnmer: a small mlecule that may bnd t ther mnmers t becme a plymer Natural fiber: Plymer: a substance cmpsed f lng chains f repeating units Synthetic fiber: Secndary transfer: the transfer f evidence such as a fiber frm a surce (a carpet) t a persn (suspect), and then t anther persn (victim) Textile: Yarn: By the end f this chapter yu will be able t: identify and describe cmmn weave patterns f textile samples cmpare and cntrast varius types f fibers thrugh physical and chemical analysis describe principle characteristics used t identify cmmn fibers apply frensic science techniques t analyze fibers Intrductin and Hw Frensic Scientists Use Fibers Very small fibers easily shed frm mst textiles and can becme trace evidence. 8

9 Fiber evaluatin can shw such things as the type f fiber, its clr, the pssibility f vilence, lcatin f suspects, and pint f rigin. Sampling and Testing Weaving spun fibers (yarns) tgether prduces Shedding frm an article f clthing r a textile is the mst cmmn frm f Natural fibers require nly an rdinary micrscpe t find characteristic shapes and markings. Infrared spectrscpy can reveal smething f the chemical structure f ther fibers that, therwise, may lk very much alike. If a large quantity f fibers is fund, sme can be subjected t destructive tests such as burning them in a flame (see analysis key abve) r disslving them in varius liquids. Crimes can be slved in this way by cmparing fibers fund n different suspects with thse fund at the crime scene. Fiber Classificatin Natural Fibers 9

10 Plant fibers (made f the plymer cellulse): can be cmmn at crime scenes because they becme brittle ver time. Plant fibers: frm seedpds is the plant fiber mst cmmnly used in textiles frm ccnuts is durable. frm stems grw in bundles. frm leaves deterirate mre quickly. Mineral Fibers: is a fibrus frm f glass. is a naturally ccurring mineral with a crystalline structure. Synthetic (artificially prduced) Fibers Until the nineteenth century nly plant and animal fibers were used t make clthes and textiles. Half the prducts prduced tday are artificially prduced. Artificially prduced fibers include 10

11 Regenerated Fibers (derived frm cellulse): is the mst cmmn f this type f fiber. It can imitate natural fibers, but it is strnger. is cellulse chemically cmbined with acetate and is ften fund in carpets. is cellulse cmbined with three acetate units, is breathable, lightweight, and used in perfrmance clthing. Synthetic Plymer Fibers: is the basis fr these fibers, and they have very different characteristics frm ther fibers. Mnmers in large vats are jined tgether t frm plymers. The fibers prduced are spun tgether int yarns. They have n internal structures, and under magnificatin they shw regular diameters. Examples f synthetic plymer fibers: fund in plar fleece, wrinkle-resistant, and nt easily brken dwn by light r cncentrated acid; added t natural fibers fr strength. easily brken dwn by light and cncentrated acid; therwise similar t plyester. inexpensive, tends t ball easily, and used as an artificial wl r fur. high perfrmance, quick drying, and resistant t wear. 11

12 Cmparisn f Natural and Synthetic Fibers Visual Diagnstics f Sme Cmmn Textile Fibers under Magnificatin Yarns, fabrics, and textiles Fibers can be twisted (spun) int yarn f any length, thick r thin, lse, r tight. A blend can be made t meet different needs such as resistance t wrinkling. Fibers can be wven int fabrics r textiles. Yarns, fabrics, and textiles Weave Patterns 12

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