Introduction to hair
Why did I decide on this topic? Well, hair is one of the most frequently found pieces of evidence at violent crime scenes. It is so easily found because hair falls out quite often and is easily pulled out of the scalp. This gives it its ability to provide a link between the criminal and the crime that occurred. However, without DNA being attached to the hair follicles, hair is considered “class evidence”, meaning that it cannot be determined just who it belongs to. However, it can limit who could be responsible for committing the crime.
Hair can also sometimes determine race, particularly if it has been treated with chemicals or if drugs have been ingested. Additionally, scientists can determine whether the hair originated from a human or an animal.
The hair shaft is composed of:
The cuticle: This is the outside covering, and it is made of overlapping scales
The cortex: This is the inner layer, which is made of keratin and embedded with pigment. It also contains air sacs called cortical fusi.
Medulla: This is the inside layer running down the center of the cortex
Looking more into the Cuticle layer:
The cuticle is the outermost layer of hair, which is covered with scales. The scales point toward the tip of the hair. Scales differ between species of animals and are named based on their appearance. The coronal cuticle type looks like straight, rugged lines, while the Spinous cuticle type looks more like a bunch of balls smashed together.
To visualize human scales on the cuticle, you must paint clear nail polish onto the glass side of the microscope, and when the nail polish begins to dry, place hair onto the polish. When the polish is almost dry, lift off the hair and observe the scale imprints.
Looking more into the Cortex layer:
The Cortex layer is what gives the keyboard its shape. It has two major characteristics:
Melanin: Pigment granules that give the hair its color
Cortical fusi: Air spaces, usually found near the root, but may be found throughout the hair shaft.
Looking more into the Medulla layer:
The Medulla layer is the hair core that is not always visible. The medulla comes in different types and patterns, including trace, interrupted, continuous, stacked, and absent (meaning there is no medulla). The human medulla is almost always interrupted, continuous, or absent.
The medullary index is determined by measuring the diameter of the medulla and dividing it by the diameter of the hair.
Thank you to Geetha S. for editing this article!