Task

Hair Lab

 

Scenario

The Crime

Sarah Smith works as a veterinarian. One evening, she had returned to work for an emergency when she heard a disturbance in the office. She followed the noise to the examination room that contains the medicine cabinet. A woman with dark hair wearing a dark jacket covered in animal fur turned from the cabinet, pushed past Sarah roughly, and exited the front door. She ran off through a neighboring wooded area. Sarah did not pursue her.

Upon inventory of the medication, Sarah found that thousands of dollars of heartworm medication were missing, along with some stronger medication that could be harmful to humans. Sarah immediately called the police.

The Victim

Police reviewed the security camera footage, but could not get a good view of the burglar's face due to her hood and hair. The police also questioned Sarah.

Sarah Smith, the victim, smiling and holding a dog.

Sarah: She was a little taller than me, maybe 5'6" or 5'7". She was wearing gloves and a neck gaiter, too, so I didn't see much, except her hair and her eyes. Her hair was shoulder-length, maybe longer? It was brown; a lot like mine. Her hoodie was covered with fur. She looked familiar.

The Evidence

Police dusted the medication room for fingerprints, but did not find any. The burglar did not leave any clear footprints. The only clear evidence from the room was hair swept up from the tile floor.

An investigator using tweezers to put hair into a plastic container.

The Suspects – Mary Brown

After speaking to Sarah, police narrowed down the suspects to three people.

Suspect 1 is Mary Brown, former partner at the clinic. Mary was fired the previous year after giving away expensive medication to friends. Mary has pet cats and dogs.

Suspect 1: Mary Brown. She is wearing a white veterinarian coat, gloves, and a stethoscope.

Mary: You want a hair sample? Sure, why not. But I would never set foot back in that place anyhow.

The Suspects – Kate Krebs

Suspect 2 is Kate Krebs. Kate has no known connection to the vet clinic. However, her husband had been caught and jailed for a series of similar burglaries at other local animal hospitals. Kate has pet cats, but is allergic to dogs.

Suspect 2: Kate Krebs. She is holding a kitten.

Kate: Burglary? That's not me, that's my husband. I'm not into that kind of stuff. I'll be happy to give you a hair sample if it gets you off my back.

The Suspects – Ashley Hicks

Suspect 3 is Ashley Hicks. Ashley works with a local dog rescue. Last week she came to the clinic asking for donations of heartworm medication and treatment for their rescues. Sarah, concerned about the crowding situation at the rescue, only offered to help if some dogs were boarded at the vet clinic. Ashley was furious and left in a rage.

Suspect 3: Ashley Hicks. She is wearing black medical scrubs and is holding a dog.

Ashley: Sarah Smith got robbed? Oh that's rich. Sure, take a hair sample. I doubt you will find anything in that mess of a clinic anyhow. And she was concerned about the condition of MY rescue?

The Forensic Lab

You're a forensic scientist in the crime lab. The detectives on this case have asked you to determine if there is any potential evidence in the hair samples they collected at the crime scene.

They are not very optimistic, since the scale used to weigh animals is also in the medication room. They are concerned that all of the samples are fur, not hair.

A forensics lab. In the lab are microscopes, laboratory flasks, and test tubes.

Examination Goals

If you do find a human sample, police may be able to perform DNA analysis.

You have two goals in your examination:

  1. Analyze the collected samples and determine if they are human.
  2. Examine any human hair found to determine if it is consistent with the samples from any of the suspects.
 

Background

Hair Structure

As you know, a hair shaft has three basic regions. Examine the hair shaft below to review.

  1. Cuticle: The cuticle is a protective coating made of overlapping scales. These scales always point toward the tip of the hair. Examination of the cuticle allows investigators to know if the hair is human or not.
  2. Cortex: The cortex gives hair its color and shape. There are three main features found in the cortex—melanin (the pigment that gives hair its color), cortical, and ovoid bodies.
  3. Medulla: The center of the hair, known as the medulla, is surrounded by the cortex. Not all hairs have a medulla. Animal hair can have special types of medulla patterns not found in humans. These distinct medulla patterns help to differentiate between human and animal hairs if there is question about the origin of the hair. It is important to note that medullae are only found in animal hair (including humans) and are never found in plant fibers!
A diagram of the microscopic structure of hair, where each part is labeled. The cuticle is the outside layer, the cortext is the second layer, which is much thicker, and the medulla is the center layer.

Differentiating Hair

You can differentiate between hair samples in several ways.

  1. Scale Patterns: You can examine the scale patterns of the cuticle to determine if the hair is human or not. There are three possible scale patterns present on the cuticle:
    • coronal (mice and rodents) Three examples of a coronal scale pattern. The scales look like stacked cups with pointy or jagged rims.
    • spinous (cats) Two examples of a spinous scale pattern. The scales are triangular and create flower petal-like rows.
    • imbricate (humans and dogs) An example of an imbricate scale pattern. The scales look like flat rectangles with squiggly sides. The surface of the cuticle looks like dried, cracked mud.

  2. Medulla Patterns: Not all human hair contains a medulla. However, there are three basic medulla types found in human hair:
    • fragmented
    • interrupted
    • continuous

    An example of the three basic medulla types. The fragmented medulla is separated into several small parts. The interupted medulla is separated only once, near the middle. The continuous medulla is not separated at all.
    By identifying a medulla type, you may determine if a hair sample is consistent with a person.

  3. Medulla Structure: The patterns within the medulla can also help distinguish what species hair is from.
    4. Drawings of what the medulla looks like in different animal species. Cats have a ladder-like medulla, deer have a lattice medulla, and rabbits and mice have medullas with multiple columns.
  4. Roots: The root of a hair can also be used to determine if a hair is animal or human.
    • cat A microscopic picture of the root of a cat hair. The root looks like it is made of little hairs or quills.

    • dog A microscopic picture of the root of a dog hair. The root is pointy like a nail.

    • human A microscopic picture of the root of a human hair. The root is round and darker at the tip.


  5. Other Features: Scientists can also examine hair for pigment granules, cortical fusi, and ovoid bodies. These patterns may help identify hair as human or animal and match samples.

Examining Hair

Hair can be examined using two different procedures:

  1. Scale Cast: Forensic scientists create an impression (or cast) of the cuticle. They can then study the scale pattern left in the cast to determine the species.
  2. Whole Mount: Scientists can mount the hair samples on a slide. This allows the scientists to examine many features of the hair, including medulla patterns and structures, roots, pigment granules, and ovoid bodies. Examination of the whole mount can help determine the species and identify similar characteristics between hair samples.

Knowledge Check #1

Which of the following characteristics can help you determine the species of a hair sample?

  1. scale pattern
  2. medulla structure
  3. root
  4. all of these

Answer: d. all of these. All of these traits can help determine the species of a hair sample.

Knowledge Check #2

Which species is this hair from? (Hint: Look at the medulla.)

A microscopic photo of a hair. The hair has a fragmented medulla. The cortex is large relative to the medulla, and the pigment is distributed towards the cuticle.
  1. dog
  2. human
  3. cat

Answer: b. human. You can tell based on the fragmented medulla. The cortex is also large relative to the medulla. Finally, the pigment is distributed towards the cuticle.

Knowledge Check #3

Why do you need to collect a sample of hair from Sarah?

Answer: You need to have her hair for comparison since she was also in the examination room with the medication cabinet.

Your Job

You will create a scale cast to determine the species of the hair samples. You will then compare the human evidence samples with samples from the suspect and victim to determine if DNA analysis is needed.

Reflection

What is the purpose of completing a scale cast analysis before examining the hair using a microscope?

 

Lab Procedure - Species ID Scale Castings

The Equipment

You will use the following equipment to examine the hair evidence.

The equipment that will be used for this lab.
From left to right: hair samples, microscope slides, cover slips, mounting medium, clear nail polish, forceps, and microscope.
  1. Hair Samples: The hair samples are kept in separate evidence bags to avoid contamination. You have hair from the crime scene plus hair samples from the suspects and Sarah Smith, the veterinarian.
  2. Microscope Slides: You will use the slides to create scale casts and for the whole mounts of the hair.
  3. Cover Slips: The cover slip protects the microscope and holds the sample in place.
  4. Mounting Medium: The mounting medium bonds the slide, sample, and coverslip together. It helps hold the sample in place.
  5. Clear Nail Polish: Clear nail polish is the medium we will use to create our scale castings.
  6. Forceps: You can use forceps (or tweezers) to handle and place the evidence.
  7. Microscope: The microscope will magnify the objects up to 40 times, allowing you to observe tiny differences in the evidence.

Procedure - Scale Castings

  1. Label the slides A, B, and C.
  2. Paint a stripe of clear nail polish onto a microscope slide.
  3. Place the appropriate hair sample on each slide with a short end of the hair extending beyond the edge of the slide. Allow the polish to dry.
  4. Remove the hair samples from the slides by pulling upward on the extended ends of the hairs.
  5. Place each slide under a microscope. Scan the scale patterns using the 4x objective (40x combined magnification), then view the samples under the 10x objective (100x combined magnification), and 40x objective (400x combined magnification).

Evidence - Scale Castings

Now that you have made your scale castings, let's see what clue they give to the species present. We know we could have cat, dog, or human hair.

The scale casting of slide A.
Scale Casting A
The scale casting of slide B.
Scale Casting B
The scale casting of slide C.
Scale Casting C
 

Evidence - Species ID Scale Castings

Viewing the Evidence

View all three scale castings below. Sketch what you see in your lab report and make notes on the scale patterns.

Sample A:

Sample A at 4x magnification. Several strands of hair were cast, but there isn't enough magnification to clearly see the scale pattern or any other defining features.
Scale Casting A at 4x magnification.
Sample A at 10x magnifiation. The hair's scale pattern is somewhat visible, which looks like repeating parallel lines going down the strand.
Scale Casting A at 10x magnification.
Sample A at 40x magnification. The hair's scale pattern is now completly visible. The scales are regular in shape, almost like cones. The scales are stacked like single blocks.
Scale Casting A at 40x magnification. Notice the regular pattern and shape of the scales.
 

Sample B:

Sample B at 4x magnification. The sample looks almost transparent at this magnification, with only a pink outline indicating where the strands are.
Scale Casting B at 4x magnification.
Sample B at 10x magnification. The scale pattern is now visible, which looks like repeating parallel lines, but not all of them connect to the other side of the hair strand.
Scale Casting B at 10x magnification.
Sample B at 40x magnification. Up close, we now see that the scale pattern looks flat. The scales are irregularly shaped, like cracked mud.
Scale Casting B at 40x magnification.
 

Sample C:

Sample C at 4x magnification. This sample also looks transparent at this magnification.
Scale Casting C at 4x magnification.
Sample C at 10x magnification. The scale pattern looks like repeating, squiggily arches.
Scale Casting C at 10x magnification.
Sample C at 40x magnifiation. Similar to sample B, the scale pattern is irregularly shaped. The scales are wavy.
Scale Casting C at 40x magnification.
 

Lab Procedure - Species ID Whole Mount

Species ID Whole Mounts

You probably were able to tell some differences between the hair samples by studying the scale castings. However, to make definitive species identifications, you will study whole mounts of the hair samples.

You will use the same equipment listed previously in the lab.

Procedure - Species ID Whole Mounts

  1. Place a clean microscope slide on a flat surface. Label the slide.
  2. Select about 5 hairs. Wet a small surface of the slide with the mounting medium. Place the hair sample in the mounting medium to secure the hair in place.
  3. Holding a cover slip horizontally in one hand, add 2 drops of mounting medium to the cover slip.
  4. Quickly invert the cover slip onto the slide starting at one edge and pivoting the other edge down. This helps eliminate trapped air.
  5. View the slide at the lowest magnification (4x objective) on the microscope, then progress down to a higher objective lens magnification (10x magnification). Finally, observe the slides at 40x total magnification.

Evidence - Species ID Whole Mount

You now have whole mounts of three different species of hair. You can compare this evidence to the scale castings to make final determinations of species for each collected sample.

The whole mount of sample A.
Whole Mount A
The whole mount of sample B.
Whole Mount B
The whole mount of sample C.
Whole Mount C
 

Evidence - Species ID Whole Mount

Viewing the Evidence

View all three whole mounts below. Sketch what you see in your lab report and make notes of your observations.

Sample A:

Sample A at 4x magnification. There are several strands of hair in the whole mount, but the magnification isn't enough to see any defining features.
Whole Mount A at 4x magnification.
Sample A at 10x magnification. At this magnification, the medulla is visible. It is continuous.
Whole Mount A at 10x magnification.
Sample A at 40x magnification. The medulla has ladder-like pattern.
Whole Mount A at 40x magnification.
 

Sample B:

Sample B at 4x magnification. The medulla is visible, but the magnification isn't enough to see any defining features.
Whole Mount B at 4x magnification.
Sample B at 10x magnification. The medulla is continuous and thick.
Whole Mount B at 10x magnification.
Sample B at 40x magnification. The medulla has a ladder-like pattern. There are ovoid boddies present in the hair.
Whole Mount B at 40x magnification.
 

Sample C:

Sample C at 4x magnification. There is no medulla.
Whole Mount C at 4x magnification.
Sample C at 10x magnification. There is no medulla. The pigment of the hair seems to get darker near the cuticle.
Whole Mount C at 10x magnification.
Sample C at 40x magnification. There is no medulla. There are also no ovoid bodies.
Whole Mount C at 40x magnification.
 

Lab Procedure and Evidence - Suspect ID

Suspect Identification

Now that we have identified which one of our hair samples is human, we can finally compare it to the hair samples from Sarah and the suspects.

The mounting process is the same as for the species ID whole mounts, so we will skip directly to the evidence.

Viewing the Evidence

Observe the evidence from the crime scene. Then, compare it with the samples from the suspects. Record your observations on your lab report.

Evidence Sample:

The Evidence Sample/Sample C at 4x magnification. The hair is brown and there is no medulla.
Evidence Sample at 4x magnification.
The Evidence Sample/Sample C at 10x magnification. There is no medulla or ovoid bodies.
Evidence Sample at 10x magnification.
The Evidence Sample/Sample C at 40x magnification. The pigment granules get darker near the cuticle.
Evidence Sample at 40x magnification.
 

Sarah Smith:

Sarah Smith's hair sample at 4x magnification. There is a medulla, but the magnification is not enough to see any details.
Sarah Smith's hair sample at 4x magnification.
Sarah Smith's hair sample at 10x magnification. The medulla is continuous and dark, almost black. The cuticle is also dark.
Sarah Smith's hair sample at 10x magnification.
Sarah Smith's hair sample at 40x magnification. There are ovoid bodies dotting the cortex.
Sarah Smith's hair sample at 40x magnification.
 

Mary Brown:

Mary Brown's hair sample at 4x magnification. The hair has a dark cuticle and a light, almost transparent cortex.
Mary Brown's hair sample at 4x magnification.
Mary Brown's hair sample at 10x magnification. THe cortex looks splotchy and is lightly colored. There is no medulla.
Mary Brown's hair sample at 10x magnification.
Mary Brown's hair sample at 40x magnification. There is no medulla or ovoid bodies.
Mary Brown's hair sample at 40x magnification.
 

Kate Krebs:

Kate Krebs's hair sample at 4x magnification. The magnification is not enough to see any details.
Kate Krebs's hair sample at 4x magnification.
Kate Krebs's hair sample at 10x magnification. The hair has a dark, reddish-brown cortex and a fragmented medulla.
Kate Krebs's hair sample at 10x magnification.
Kate Krebs's hair sample at 40x magnification. The medulla, cortex, and cuticle are all dark brown and they blend in with each other. Unlike the other samples, the edge of the cuticle is not obvious.
Kate Krebs's hair sample at 40x magnification.
 

Ashley Hicks:

Ashley Hicks's hair sample at 4x magnification. The hair strands are brown and there is no medulla.
Ashley Hicks's hair sample at 4x magnification.
Ashley Hicks's hair sample at 10x magnification. There is no medulla or ovoid bodies.
Ashley Hicks's hair sample at 10x magnification.
Ashley Hicks's hair sample at 40x magnification. The pigment granules get darker near the cuticle.
Ashley Hicks's hair sample at 40x magnification.

Analysis

At this point, you should have enough information to identify a suspect. Complete your lab report, being as specific as possible with your observations. Don't forget to include your suspect, if you were able to identify one!

Remember to complete your lab report! Your findings will be shared with law enforcement and used, in part, to resolve or move this case forward.