Hair and Fiber Lab
Background: Often, forensic scientists need to determine the characteristics of items
found at a crime scene and compare these items to ones found on a suspect or at the
suspect's home, car, boat or anything connected to the suspect. Physical Properties of
trace substances can be used to describe and compare these items of criminal interest.
The Locard Principle states that if one surface touches another, there will be an exchange
of some physical material, which can be identified. Hair and Fibers are examples of these
types of material. Hair and fiber evidence is often used to identify victims and/or suspects
from a crime. These crimes can include murder, sexual assault, hit and run accidents and
burglary. Not only can be used to identify people, it can show the entrance or exit route of
the perpetrator. Hair and fibers can be used to identify clothes or shoes, or any other item
belonging to the suspect. Common characteristics of hair include color, continuous or
fragmented medulla, with of hair, artificial coloring and recognizable textures. Hair can be
identified from humans or different animals. If human, further DNA testing can be
performed if the root containing DNA is attached to the hair.
Hair structure: The hair grows from follicles in the skin and covers the surface of
mammals. A small muscle that helps the hair stands up surrounds each follicle. A nerve
connects the hair follicle to the brain with a sebaceous gland next to the follicle producing
sebum, an essential oil. The hair is embedded in the skin follicle at the root and extends
the length of the hair shaft. A cross section of a hair includes the cuticle on the outside
next to the cortex and finally the inner core is called the medulla. Most of the hair is
cortex, which contains the color pigments.
Forensics scientists first determine if the hair is human or animal, then compare to
suspect’s hair or known pets. A comparison microscope works best for this analysis.
Essential Question:
What are the different distinction characteristics of hair and fibers?
Purpose: To identify hair from different animals and people in order to match hair from a
crime scene to an individual person or animal. In addition, different types of fibers are
identified.
Safety Precaution: allergies to latex, xylene (in Kleermount)
Equipment:
Microscopes
Microscope slides, cleaned with soapy water and an alcohol rinse, dry with lens
paper or Kim Wipes and/or lens paper
Cover slips
Forceps
Hair samples from the kit and other collected specimens include horse, rabbit,
deer, dog, and cats
Bat hair slide (very interesting) from Cargille labs
Fibers (wool, cotton, nylon) from Cargille labs
Reagents:
dropper bottle of water
dropper bottle of glycerin
1 dropper bottle of latex
Kleermount with xylene
Alcohol, 70% isopropyl alcohol
Procedure:
1. Clean slides with warm soapy water, rinse with alcohol and dry with Kim wipes
or lens paper. Label each slide prior to adding the sample of hair or fiber,
include the name of the type of slide you are making.
2. Three types of slides can be made: a. wet mount, b. a scale cast and c. a whole
mount slide. The scale cast and whole mount slides need to be prepared 24
hours in advance.
3. Wet mount slides: Obtain a sample of hair or fiber and place on clean slide with
forceps, add a drop or two of glycerin or water, cover with cover slip and view in
microscope.
4. Scale cast: Place a drop of latex near the end of clean slide and with a second
slide pull the latex along the slide into a thin film, immediately add several
strands of a specific hair or fiber to the film of latex. Let dry overnight. Once
latex is hard, use forceps to remove the hair and examine the scale cast left
from the hair or fiber under the low power objective. Do not use high power
objectives.
5. Whole-mount slides: Place a drop of Kleermount in the center, add several
strands of hair or fiber to the Kleermount, and cover with cover slip. Leave for a
day to dry, before viewing.
6. Sketch each type of hair or fiber and label each slide: note color and patterns in
data table.
Hair Data Table:
Color
Shape
Medulla
pattern
(continuous
or broken)
Bleached
or Dyed
Probable
source
1.
2.
3.
4.
Fibers:
Color
Patterns
Shape
1. Wool
2. Cotton
3. Nylon
4. Unknown
Questions:
1) Compare and contrast the different types of hair characteristics from different
ethnic groups of people.
2) Compare and contrast the different types of hair characteristics from different
animals.
3) Compare and contrast characteristics of the different fibers.
Conclusion:
Discuss the results of the suspects’ hair to the known hair sample. Whose hair
was it?
Hair
http://www.natural-hair.com/structure.html (nice figure of hair structure)
http://www.naturalhaircolor.com/natural-structure-of-hair/
(discusses hydrogen bonds and beta structure of the hair)
http://www.ivy-rose.co.uk/HumanBody-Images/Structure_of_Skin/HairFollice-Qu.jpg
For answers
http://www.ivy-rose.co.uk/HumanBody/Skin/Hair-Follicle.php
http://www.ivy-rose.co.uk/HumanBody/Skin/Hair-Follicle.php
1. _______________________
7. _______________________
2. _______________________
8. _______________________
3. _______________________
9. _______________________
4. _______________________
10. _______________________
5. _______________________
11. _______________________
6. _______________________
12. _______________________
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Hair Follicle
Hair follicles are the structures from which hairs emerge from the skin. Each hair is a
thread of fused (i.e. attached together), dead, keratinized cells. The two main parts of
hairs are:
• The hair shaft is the visible part of the hair that protrudes through the skin.
• The hair root is the part of the hair below the surface of the skin that includes and/or
interacts with many other associated structures within the dermis and hypodermis
layers of skin.
tructures of a Hair Follicle
Hair shaft
- Hair shaft is the visible part of the hair that protrudes through the skin. It consists of layers of fus
keratinized cells.
Medulla
- The innermost layer of a hair is called the medulla. A medulla is not present in all hairs, only in
e.g. protruding from the scalp rather than from the abdomen or upper-arms (where hairs tend to b
dense).
Cortex
- The middle layer of hair is the cortex. This provides strength and determines both the colour an
hair.
Cuticle
- The outermost layer of hair is the cuticle. This is a thin colourless layer that protects the cortex
Hair root
- The hair root is the part of the hair lying below the surface of the outer-layer of skin (i.e. the epid
hair root therefore includes many of the main structures of the hair, incl. the bulb, papilla and g
Dermal root
sheath
- The dermal root sheath, which is sometimes referred to as simply the "root sheath" is compose
epidermal cells called:
• the external epithelial root sheath (see below), and
• the internal epithelial root sheath (see below)
These two layers are surrounded by an outer sheath of connective tissue.
Arrector pili
muscle
- The arrector pili muscles associated with hair follicles consist of smooth muscle (as these musc
unconscious, rather than conscious control). The arrector pili muscle associated with each hair
the side of the hair follicle to the outermost (i.e. towards the surface of the skin, or upper - as sho
the dermis layer of the skin.
When at rest the arrector pili muscle is extended and the hair shaft emerges from the skin at a
However, when the body is under some form of stress, e.g. due to fear or low temperatures, the n
autonomic nervous system) stimulate the arrector pili muscles to contract, which in turn pulls th
that the hair shaft emerges from the surface of the skin at closer to 90o, i.e. perpendicular to the
This also results in slight elevations of skin where each hair shaft emerges - as is colloquially refe
pimples" (British English) or "goose bumps" (American English).
Sebaceous
- Sebaceous glands are accessory structures of the skin. Most sebaceous glands are connected to
gland
Hair bulb
secret an oily substance called sebum, whose functions include:
• preventing the hair from becoming too dry
• preventing surrounding skin from becoming too dry (due to evaporation of water from the skin),
the skin soft
• inhibiting the growth and reproduction of some bacteria
- The base of the hair follicle is a bulb-shaped structure called the hair bulb. This includes several
types of cells that extend up through the hair follicle, an indentation called the papilla (of the hair
region of cells called the germinal matrix.
External
epithelial
root sheath
- The external root sheath consists of several layers of cuboid epithelial cells visible when stained
histology stains for more about this and other stains).
Internal
epithelial
root sheath
- The internal root sheath consists of three layers: Henle's layer, Huxley's layer, and an internal cu
continuous with the outermost layer of the hair shaft.
Germinal
matrix
- The germinal matrix is sometimes referred to as simply the "matrix" when the context of hair fol
ambiguity. This is the area of cells that produces new hairs (by the mitosis process of cell division
hairs are shed.
Papilla
- The papilla of the hair contains many blood vessels (the diagram above is a simplified represen
there is are many tiny inter-connected vessels not just the one shown). These blood vessels supp
nourish the growing hair.
Hypodermi
s layer
- The sub-cutaneous layer (also known as the hypodermis layer) of skin consists of adipose tissue
connective tissue. It's function is to attach the skin to the underlying structures of the body. As sh
skin includes many fat cells. It acts as a storage reserve for fat cells and also contains and protec
vessels, including arteries and veins that supply hair follicles.
Artery
(blood
supply)
- Blood supplied to tissues, from the heart, travels under higher pressure than blood drained from t
Oxygenated blood and other nutrients are supplied to tissues and cells in the body via the arte
dermis and hypodermis layers of the skin and the arterioles (tiny branches of arteries that lead to
from them.
Vein
(blood
drainage)
- Blood drained from tissues, for return to the heart, travels under lower pressure than blood suppli
Deoxygenated blood and waste products (from the reactions of metabolism) are returned to th
within the dermis and hypodermis layers of the skin and the venules (tiny branches of veins leadi
leading to them.