chapter 3 the study of hair -...

Forensic Science: Fundamentals & Investigations, Chapter 3 1

Chapter 3 The Study of HairBy the end of this chapter you will be able to:

identify the various parts of a hair

describe variations in the structure of the medulla,

cortex, and cuticle

distinguish between human and nonhuman hair

determine if two examples of hair are likely to be from

the same person

explain how hair can be used in a forensic investigation

calculate the medullary index for a hair

All Rights Reserved South-Western / Cengage Learning © 2009


History of Hair Analysis

1. Alfred Swaine Taylor and Thomas Stevenson, in 1883, wrote a forensic science text that included a chapter on hair.

2. Victor Balthazard and Marcelle Lambert, in 1910, published a comprehensive study of hair.

3. Dr. Sydney Smith, in 1934, first used a comparison microscope to analysis hairs side by side.

4. Advances continue today with chemical tests, neutron activation analysis, and DNA analysis.


The Function and Structure of Hair

Hair on mammals helps to regulate body temperature, decrease friction, and protect against sunlight.

Hair consists of (a) a hair shaft produced by (b) a follicle embedded in the skin.

A hair has three layers (illustrated above): the inner medulla, the cortex, and the outer cuticle.


Types of Cuticle and CortexThe Outer 2 Layers

The Cuticle is the outermost layer made of over-lapping scales that protect the inner layers of the hair.

The Cortex is the thickest layer containing most of the pigment giving hair its color.

The distribution of pigment in the cortex varies from person to person.

Pigment, commonly, is denser nearer the cuticle.


Types of Medulla

The medulla (the inner section) can be hollow or filled, absent, fragmented, continuous, doubled, pigmented, or un- pigmented.


The Life Cycle of Hair

Hair proceeds through 3 stages as it develops:

1. During the long anagen stage, hair actively

grows. The cells around the follicle rapidly

divide and deposit materials in the hair.

2. In the catagen stage, the hair grows and

changes.

3. Hair is in the telogen stage when the follicle

becomes dormant. During this stage, hairs

easily can be lost.


Racial Differences

Hair examiners have identified some physical characteristics that generally can be associated with broad, racial groups.

These characteristics, however, will not apply to all individuals in these groups.

In addition, at times, it will be impossible to assign specific hairs to any of these groups be-cause their characteristics are poorly defined or hard to measure.


Animal Hair and Human Hair

Core: the medulla -- Thickest layer: the cortex --Outermost: the cuticle

Pigmentation in animal hair is denser toward the medulla. In Humans it tends to be denser toward the cuticle.

Unlike human hair, animal hair abruptly can change colors in banded patterns.

The medullary index is different. In animals the medulla is much thicker than it is in humans.


Animal Hair and Human Hair

Spinous Coronal ImbricateThe outermost layer of the hair shaft (the cuticle), is typically different in animals and humans.

– The cuticle scales in animals tend to resemble petals (spinous) or they give the appearance of a stack of crowns (coronal).

– The cuticle scales in humans commonly are flattened and narrow (imbricate).


Using Hair in an Investigation

Macroscopic investigation can indicate length, color, and curliness.

Microscopic investigation can indicate fine detail in hair structure.

– Phase contrast microscopy, for example, can show the presence of dye or other treatments.

– Electron microscopes can provide more detail of the surface or interior of the sample. In the sample above, note the overlapping scales and the pigment granules in the cortex.


Testing for Substances in the Hair Shaft

1. Chemicals that the skin absorbs often can be detected by analysis of the hair shaft.

2. A forensic scientist can perform chemical tests for the presence of various substances.

3. The hair shaft can be examined in sections to establish a timeline for exposure to toxins.

4. Neutron Activation Analysis (NAA) can determine concentrations of substances in the sample.


Testing the Hair Follicle

Microscopic assessment of the follicle is performed first because it is cost effective and quick.

– If a microscopic match is found, the follicle can be blood tested and perhaps show the blood type.

– If a microscopic match is found, the follicle can be DNA analyzed to provide identification with a high degree of confidence.


. . . . . . . . . . . . . . . . . Summary

Hair consists of a (a) hair shaft produced by a (b) follicle embedded in the skin.

The shaft consists of an outer cuticle, a cortex, and an inner medulla.

Various hair treatments produce characteristic effects useful to forensic experts.

Some characteristics allow them to be grouped into general racial categories.

Forensic experts examine hair using chemicals, light, electrons, neutrons, and DNA sequencing.


Chapter 4 A Study of Fibers and Textiles By the end of this chapter you will be able to:

identify and describe common weave patterns of textile samples

compare and contrast various types of fibers through physical and chemical analysis

describe principle characteristics used to identify common fibers

apply forensic science techniques to analyze fibers

All Rights Reserved South-Western / Cengage Learning © 2009


Introduction and How Forensic Scientists Use Fibers

Fibers often fall off and are picked up during normal activities.

Very small fibers easily shed from most textiles and can become trace evidence.

In an investigation, collection of fibers within 24 hours is critical.

Fiber evaluation can show such things as the type of fiber, its color, the possibility of violence, location of suspects, and point of origin.


Sampling and Testing

Weaving spun fibers (yarns) together produces clothing and many textiles.

Shedding from an article of clothing or a textile is the most common form of fiber transfer.

Natural fibers require only an ordinary microscope to find characteristic shapes and markings.

Infrared spectroscopy can reveal something of the chemical structure of other fibers that, otherwise, may look very much alike.


Sampling and Testing

If a large quantity of fibers is found, some can be subjected to destructive tests such as burning them in a flame (see analysis key above) or dissolving them in various liquids.

Crimes can be solved in this way by comparing fibers found on different suspects with those found at the crime scene.


Fiber Classification —Natural Fibers

woven wool textile Animal fibers (made of proteins):

Wool from sheep, cashmere and mohair from goats, angora from rabbits, and hair from alpacas, llamas, and camels are commonly used in textiles.

Shimmering silk from caterpillar cocoons is longer and not as easily shed.



Plant fibers (made of the polymer cellulose):

can absorb water.

are insoluble in water.

are very resistant to damage from harsh

chemicals.

can only be dissolved by strong acids.

can be common at crime scenes because

they become brittle over time.



Plant fibers:

Cotton from seedpods is the plant fiber most commonly used in textiles (shown above).

Coir from coconuts is durable.

Hemp, jute, and flax from stems grow in bundles.

Manila and sisal from leaves deteriorate more quickly.

Mineral Fibers:

Fiberglass is a fibrous form of glass.

Asbestos is a naturally occurring mineral with a crystalline structure.


Fiber Classification —Synthetic (artificially produced) Fibers

Until the nineteenth century only plant and animal fibers were used to make clothes and textiles.

Half the products produced today are artificially produced.

Artificially produced fibers include rayon, acetate, nylon, acrylics, and polyesters.



Regenerated Fibers (derived from cellulose):

Rayon is the most common of this type of fiber. It can imitate natural fibers, but it is stronger.

Celenese® is cellulose chemically combined with acetate and is often found in carpets.

Polyamide nylon is cellulose combined with three acetate units, is breathable, lightweight, and used in performance clothing.



Synthetic Polymer Fibers:

Petroleum is the basis for these fibers, and they have very different characteristics from other fibers.

Monomers in large vats are joined together to form polymers. The fibers produced are spun together into yarns.

They have no internal structures, and under magnification they show regular diameters.


Fiber Classification—Synthetic (artificially produced) Fibers

spandex nylon

Examples of synthetic polymer fibers:

Polyester—found in “polar fleece,” wrinkle-resistant, and not easily broken down by light or concentrated acid; added to natural fibers for strength.

Nylon—easily broken down by light and concentrated acid; otherwise similar to polyester.

Acrylic—inexpensive, tends to “ball” easily, and used as an artificial wool or fur.

Olefins—high performance, quick drying, and resistant to wear.


Comparison of Natural and Synthetic Fibers

Visual Diagnostics of Some Common Textile Fibers

under Magnification


Yarns, fabrics, and textiles

Fibers can be twisted (spun) into yarn of any length, thick or thin, loose, or tight. A blend can be made to meet different needs such as resistance to wrinkling.

Fibers can be woven into fabrics or textiles.

– Threads are arranged side by side (the warp).

– More threads (the weft) then are woven back and forth crosswise in one of a number of different patterns through the warp.


Yarns, fabrics, and textiles

Weave Patterns


. . . . . . . . . . . . . . . . . Summary

Fibers are spun into yarns having specific characteristics.

Yarns are woven, with different patterns, into clothing or textiles.

Fibers, trace evidence, are a form of class evidence used by crime scene investigators.

Fiber evidence may be gathered using different techniques.

Fibers may be analyzed using burn tests, tests for solubility in different solutions, polarized light microscopy, or infrared spectroscopy.

chapter 3 the study of hair -...

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