chapter 3 the study of hair - marblehead high school science...7 forensic science: fundamentals...

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

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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.


Types of Hair

Buckled Blunt Double Medulla The cross section of a hair can be circular, triangular,

irregular, or flattened influencing the curl of the hair. The texture of a hair can be coarse or fine. Different regions of the body on which hair can vary are

(1) head, (2) eyebrows and lashes, (3) mustache and beard, (4) underarms, (5) overall body (auxiliary hair), and (6) pubic.


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.


Treated Hair

Forensic investigators sometimes can link hair from a location with an individual. – Bleaching disturbs the scales on the cuticle and

removes pigment leaving hair brittle and a yellowish color.

– Dyeing colors the cuticle and the cortex of the hair shaft.

Because of this and because hair grows daily, a person’s treated hairs will have specific char-acteristics in common with her or his lost hairs.


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 3 the study of hair - marblehead high school science...7 forensic science: fundamentals...

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