INTRODUCTION

One of the most recovered types of evidence is also one of the most misunderstood. Hairs make good forensic evidence because they are sturdy and do not degrade easily and hence can survive for many years, they carry a lot of biological information, and they are easy and cost-effective to examine. Hair examinations have further forensic significance as DNA can be extracted from them. Hairs can offer strong investigative and adjudicative information, but only when examined properly, reported on conservatively, and testified to accurately.

Growth of Hair is a feature that is characteristic of mammals; It is the fibrous growth that originates from the epidermis of the skin. Other animals have structures that may appear to be or are even called hair, but they are not. E.g., Whiskers on a Catfish.

STRUCTURE OF HAIR

A hair is a complex, filamentous biomaterial comprising of various intricately organized structures. Only some of these structures can be observed under a microscope. A single hair strand on a macro-scale has a root, a shaft, and a tip. The proximal-most portion of the hair is the root, it is that portion that was formerly was in the follicle. The main portion of the hair is called the shaft. The distal-most portion of the hair is called the tip. Internally there are three main structural layers in a hair, namely the cuticle, the cortex, and the medulla. The outer layer of the hair shaft is termed the cuticle. It consists of a series of overlapping layers of flat, thin scales that form a protective covering. The scale patterns present in human beings are called imbricate, but it is fairly common among animals and, despite many attempts to use scales as an individualizing tool for human hairs, this has proven to have very less forensic utility. The Cortex is the region located between the cuticle and medulla layer. It makes up the bulk of the hair and it contains pigment granules that are dispersed variably throughout the cortex. They vary in size, shape, assemblage, and distribution and hence prove excellent for forensic comparisons. The width of the cortex in human beings is less than that of the medulla. The central part of the hair is termed as the medulla. It is made up of loosely connected cells that are comparatively large in size. These cells contain Keratin. Based on the appearance, it is divided into five types- Continuous, interrupted, fragmented, solid, and absent. Human beings mostly have interrupted or absent medulla. The medullary index in humans is usually less than 1/3. 

Source: https://www.sheainstitute.com/asbi-library/hair-anatomy/

DETERMINATION OF RACE

HUMAN AND ANIMAL HAIR

BODY AREA DETERMINATION

Humans exhibit a wide variety of hairs on their bodies, unlike other animals. The body area origin can be estimated by the characteristics displayed by this hair. The typical body areas that can be determined are the scalp, pubic, vulvar, chest, beard, axillary, eyelash, nose, limb, and buttocks. Usually, only scalp and pubic hairs are suitable for microscopic comparison. Hairs that do not fit into these categories are classified as transitional body hairs E.g. Hair present between the chest and pubic region. Analysts usually find it hard to differentiate between chest and axillary hair. But terming all of them as body hair while filing a report is usually sufficient.

Source: https://books.google.com.au/books?id=8dicBAAAQBAJ

The macroscopic traits that can be observed in the hair are-

●       Colour- White, blonde, red, brown, black, and other.

●       Hair form- Straight, curved, waved, curled, kinked.

●       Diameter- fine, medium, coarse, variations.

●       Length

The microscopic traits that can be observed in the hair are-

●       Colour- Natural/treated

●       Pigmentation- distribution, Aggregation (density, size), granule (colour, size, shape, density)

●       Structure- diameter, artificial treatments, shape (cross-section, configurations), acquired hair (root shaft [cortex, cuticle, medulla], Tip), diseases.

SAMPLING OF HAIR

●       The exhibit should be spread on a clean white surface under proper illumination. Any loose hair is carefully located and collected with the help of a hand magnifier.

●       Hair can be collected using forceps or can be tape lifted using adhesive tape.

●       The collected samples should be packed in cellophane or paper folders with proper labeling on them.

●       The follicle of hair and the root bulb should be carefully preserved for determination of sex, and further serological and DNA examination.

EXAMINATION OF HAIR

1. Temporary mount– A temporary mount of the hair sample is made on a clean slide using distilled water or glycerine solution. It is covered with a coverslip and the morphological structures of the hair are observed under a microscope.
2. Scale Casting-

●       Cellulose Acetate method- A thin layer of cellulose acetate paste that has low viscosity is placed on a clean microscopic slide. Using forceps, the hair is placed onto the paste and is pressed with another clean slide. It is allowed to dry for 2-5 minutes and the scales of the hair can be microscopically observed.

●       Polaroid Coater Method- The hair sample is placed on a clean microscopic slide and the ends of the strand are secured with cellophane tape. A polaroid film coater is applied 2-3 times along the length of the hair. This coating is allowed to dry for 23-24 hours. After the cellophane tape is removed, the hair is gently peeled from the slide. The excess coating that protrudes above the flat surface of the cast is sliced away with the aid of a sharp scalpel. Now, the impressions of the scales can be microscopically observed.

3. Permanent mount- The hair sample is placed on a clean slide in a drop of xylene and a few drops of the permanent mounting medium are added. A cover-slip is placed, the slide is labeled appropriately, and is allowed to dry for 48 hours.
4. Cross sectioning- The hair sample is placed in a solution of ether and ethanol in the ratio 1:1. The samples are bundled and dipped in a block of molten wax and is then allowed to cool. Cross-sections can either be taken using a sharp blade or with a microtone to a thickness of 5-10 microns. These sections are placed on a clean slide and the wax is dissolved with a drop of xylene. A permanent mount of the sections is prepared and then examined under a microscope. The cross-section of straight hair is fairly circular and gets increasingly oval for wavy and curly hair.
5. Micrometry- Various lengths, distances, and indexes can be calculated with the help of a micrometer.

●       The maximum diameter of the hair shaft, medulla.

●       The number of scales per unit length.

●       The medullary index.

DNA EXAMINATION OF HAIR

DNA in hair is usually extracted from the root bulb, as it contains a major part of the evidence and may also contain trace amounts of skin. This is common if a violent crime has taken place as hair could have been forcefully uprooted by both the victim and the perpetrator during a physical struggle. But in the absence of the root, DNA typing is directed towards the mitochondrial DNA present in the hair sample, instead of nuclear DNA. Mitochondrial DNA is present in large quantities in each cell and unlike nuclear DNA which is received from both parents, mitochondrial DNA is only received from the mother. This is extracted, amplified and the obtained DNA sequence is run through a criminal database.

The combination of Microscopic and DNA examinations will give us superior knowledge as compared to only the latter. There have been various erroneous convictions in the past due to the absence of efficient DNA extraction tools, this drawback has largely been overcome nowadays.

REFERENCES

1. Fundamentals of Forensic Science- Max M. Houck, Jay A. Siegal
2. An international survey into the analysis and interpretation of microscopic hair evidence by forensic hair examiners- Laura Wilkinson, Claire Gwinnett
3. Forensic Examination of Hair- Bhoopendra Singh Bhaskar

-Kamali Saravanan

Forensic Science Honors, Jain University