Lab 3 – Hair Analysis
Theory:
Forensic scientists have to determine whether a hair found at a crime scene is a human or animal
hair. If it is human, they compare it with the hairs of suspects to see if they can make a match. If it is
animal, they try to identify the animal species.
If the hair under investigation is human, the part of body from which it originated. Also, scientists
can sometimes determine the race of the person from samples of his or her hair. In addition to what we
discussed in class, the hairs can be distinguished by the medulla. In both Negroid and Caucasoid hairs,
the medulla is discontinuous or absent; however, Mongoloid hairs have a continuous medulla.
Hair grows from follicles in the skin, which cover the entire surface of mammals. Located beside
each follicle is a small muscle that can make the hair stand upright. A nerve connects the follicle to the
brain. A sebaceous gland in the wall of the follicle produces sebum, which is an oil essential for normal
hair and skin. The entire length of a hair includes at the root, which is imbedded in the skin follicle.
A hair is composed of three distinct layers: cuticle, cortex, and medulla. The cuticle is the hard,
outside covering that protects the inner layers of the hair. It is made of overlapping scales pointing
toward the tip. The scales are cells that have hardened and flattened. There are many different types and
arrangements of scales, from loose, open scales to tight, firm scales.
The cortex is made of cells within the cuticle. Three quarters to 90% of a human hair is composed
of cortex. These cells contain pigments that pigments that give the hair its color.
The medulla is made of cells that run through the center of the cortex like a canal. In humans, this
is a very small layer. The medulla may not be a continuous canal: it can be interrupted, fragmented, or
absent. Forensic scientists can determine the medullary index of a hair: the diameter of the medulla
relative to the diameter of the hair. Humans have a medullary index of less than one-third. The
medullary index of animals is usually one-half or greater.
The shape or pattern of the medulla can help scientists determine its source. In many animals, the
medulla makes up most of the cortex. Note the difference in the picture below.
Objective:
You will compare different types of hair under the microscope and you will analyze the medulla,
cortex, and cuticle of several hair samples.
Background Story:
Jane Menendez owns a cat, Stingray, who has starred in several commercials for Fancy Fresh Cat
Litter. Before Stingray was a famous cat, he belonged to Polly Jones, a full-time college student. Jane
agreed to take the cat from Polly a few years ago when Polly was too busy to properly care for him. Since
Stingray’s recent introduction to the world of TV, he has earned his owner about $750,000.
On May 2, Ms. Menendez called the Durham police to report that Stingray had been stolen.
Menendez states that she was in the family room watching the 10 pm news while Stingray ate his dinner
in the kitchen. Menendez heard the door open and then heard a loud screech from the cat. By the time
she got to the door, Stingray was gone and all she saw was medium sized car speeding away from her
home.
Investigators at the scene found no signs of forced entry. Police asked Ms. Menendez for a list of
people who drive a medium sized car and have a key to the house. Her list includes:
A. John Menendez, her husband, who loves dogs and is allergic to cats.
B. Bob Barlow, a cosmetics salesman whose products are boycotted by Ms. Menendez because they
are tested on animals. Sue Barlow, his wife, is one of Jane’s best friends and knows where the
spare key to the hose is hidden.
C. Jillian Roman, a neighbor and cat hater who has poisoned several cats in the neighborhood. Since
Jillian’s kitchen window looks into Jane’s backyard, Jillian may have seen Jane hide her spare key.
D. Bethany Bledsoe, the maid who often complains that Stingray sheds hair all over the house.
Bethany has her own key.
E. Polly Jones, Stingray’s previous owner and part time sitter. Polly keeps a key for those occasions
when she cat-sits. Neither Bob, Jillian, Bethany, nor Polly owns a cat. Later that night, police
comb the interiors of their cars to see if they can find any cat hairs.
Procedure:
1. Prepare a we mount slide of a piece of hair from one of the envelopes by placing the hair on the
slide, adding a drop of water to the hair, and covering the hair and water with a cove slip.
2. Examine the hair under low, medium, and high powers. Draw what you see on high power on a
table similar to the one below in your lab book.
Sample A
Sample B
Sample C
Sample D
Sample E
3. Estimate the medullary ratio of each hair. Include this in the next data table.
4. Note the hair length, tip condition, and shape of the root.
Sample A
Sample B
Sample C
Sample D
Sample E
Medullary
Ratio
Hair length
Tip condition
Root condition:
absent,
rounded,
tapered
Any other
noticeable
features
5. Repeat the steps for each of the remaining hairs.
Post Lab Questions:
1. Based on the information in your sketches and in the data table, which hair sample(s) belong to
Stingray?
2. How can you tell the animal hair from human hair?
3. When examining the hairs under the microscope, were the cuticle scales clearly visible? Describe
their appearance.
4. Write a brief story describing the crime.