Hair is one of the common and important physical evidence encountered in crime scene. The evidence establishes the presence of culprit at the scene of occurrence. Mutual transfer of hair due to contact may be a classic example of Locard’s principle of mutual exchange of traces hair.  The hair is examined visually and microscopically. The microtomy is used for cross sectional examination of hair.

VISUAL EXAMINATION OF HAIR

Visual examination of hair reveals the color, length and general condition of hair. It may give an idea of whether the hair has been dyed or not. It also indicates the presence or absence of contaminants and their nature.  Hand magnifiers and stereo microscopes improve visual examination of hair.

MICROSCOPIC EXAMINATION OF HAIR

Light microscopy is used for examination of hair in forensic laboratory. Two steps are followed in this examination: identification of questioned hair and comparison of questioned hair with known hair. Various steps involved in examination of hair. First examination is to see whether the hair belongs to human or animal. If it belongs to animal, then which animal it is possible to identify the species of animal.

The various microscopes used for examination of hair are:

  1. Stereomicroscope
  2. Compound microscope
  3. Phase contrast microscope
  4. Comparison microscope
  5. Scanning electron microscope

The stereo microscopes are used with magnification up to 100X for initial examination of mounted or unmounted hair.  It reveals their color, contamination, characteristics or whether roots are present or not. It is possible to say whether the hairs have been pulled out, cut or fallen. Pulled out hairs have live bulbs and sign of stretching near the bulb. The detailed microscopic examination of hair is done after cleaning them in the alcohol-ether mixture (or acetone). They are mounted on microscopic slide and examined under magnification (400X). The examination of hair under microscope reveals:  

  1. Actual color of hair: the contamination which may be masking the original color of the hair is removed in the cleaning process.
  2. Dying or bleaching treatment: whether the hairs have been dyed or bleached. Natural color of hair is found near the starting point. This portion of hair may be long or short depending upon the period elapsed between the dying or bleaching and collection of hair for examination.
  3. Morphology of hair: it indicates the presence or absence and nature of the medulla and the pigmentation pattern.
  4. The body part from where which the hair originated: the head hair like rods, whereas the hairs from eyebrows or eyelashes have pointed ends or tips, the beard hair may be flattened.
  5. Pigment distribution: it is helpful in the study of species of origin and in the identification of hairs of an individual. It is often an important characteristics and permits elimination of certain suspected sources of hair.
  6. Medullary index: the ratio of diameter of hair to the shaft of the hair is called as medullary index. It indicates the species of origin, as the medullary index of human hair is commonly less than 0.3 and in animal it is more than 0.5.
  7. Roots and ends: they reveal whether the hair have been pulled out or not. Whether they are cut and if so once they were last cut.  Freshly cut tips hairs have sharp cut edges. Over the time, tips or root ends become round. 
  8. Vacuoles
  9. Deformity or diseases in the hair.
examination of hair

DIFFERENT TYPES OF HAIR

The diversity of various kinds of hair is enormous, from lean curls to ruler straight. The pigment and form of hair differ. The type of hair you have is genetic from your ancestors. It although rest on the race, or mixture of races, from which they came.  Scientists have identified three types of hair in today’s human population: Asian, Caucasoid and African.

CAUCASOID (EUROPEAN): hairs of Caucasoid origin can be of sufficient to medium coarseness, are usually straight or wavy in look and have color ranging from  pale brown to black. The hair strand of Caucasian hairs differs from round to oval in cross section and has reasonable to medium-sized, consistently distributed pigment granules.

MONGOLOID (ASIAN): Hairs of Mongoloid or Asian origin are frequently rough, straight and round in cross-section. The outer coating of the hair, the cuticle, is typically denser than the cuticle of Negroid and Caucasian hairs and medulla is continuous and wide. Mongoloid hair can have a distinctive reddish look as a product of color grain pigments.

NEGROID (AFRICAN): hairs of Negroid or African origin are repeatedly curly or kinky, have compressed cross section and look like curly or wavy. Twisted hair shaft, known as buckling.

DIFFERENCE BETWEEN HUMAN AND ANIMAL HAIR

The comparison microscope is used to examine comparison between the known and questioned hair sample. The range of magnification commonly used is app 40X to 400X. A glass microscope slide with known or reference of hair sample is placed on the stage of microscope.

Following are the characteristics that are observed when microscopic examination of hair is done to check whether the hair belongs to human or animal.

S. NoCHARATERISTICSHUMAN HAIRANIMAL HAIR
1CUTICLEScales are small, flattened and surround the shaft completely Scales are large, wavy and do not surround the shaft completely
2MEDULLANarrow, discontinuous or fragmentedBroad, always present and continuous
3CORTEXThick, width of the cortex greater than medullaThin, width of cortex less than medulla
4MEDULLARY INDEXLess than 0.3 or 1/3More than 0.5 or ½
5 DISTRIBUTION OF PIGMENTMore  towards the periphery of the cortex/ towards cuticleUniform, peripheral or central / towards medulla

MICROTOMY

The cross sections of hairs are obtained with the help of an instrument called microtome. Clean hair is embedded in hair wax, plastics or flesh. It is sliced into thin circles. The slices are fixed in Canada balsam on a microscope slide after cleaning them with acetone and the cross –sectional structure of hair is studied.

Microtomy is helpful in the microscopic study of the cross-section of the hair to determine pigment distribution, medullary shape and medullary index of the hair. Cross sectioning also, facilitates the proper study of the shape of the hair and relative sizes of the hair parts: medulla, cortex and the cuticle.

NEUTRON ACTIVATION ANALYSIS

The qualitative and quantitative examination of the element such as arsenic, iron, lead and silicone present in the hair permit the identification of the possible common source hair because the composition varies from one individual to other. It does not individualization of the person. The technique is simple in principle. In examination of hair, the hair is exposed to neutron bombardment. The trace elements in the hair become radioactive. Gamma- rays spectrometry gives qualitative and quantitative analyses. Comparison of the analyses of the questioned and the standard sample indicates the possible common/ different source.

SCANNING ELECTRON MICROSCOPY

Scanning electron microscopy is playing an increasingly important part in the examination of hair structures. The instrument has been applied particularly for the study of cuticles/ scales structure. They are studied with the instrument in both ways, direct or after preparing the casts of the hair.

DNA profiling

If the skin, flesh or blood was sticking to the hair root, define identification of the source person of the hair is made through nDNA profiling. However, hair in criminal situations is usually fallen hair. They do not carry sufficient body cell materials and thus fail to provide the nDNA profiling. However, the discovery of mitochondrial DNA has changed the scenario. Now, hair can be linked to an individual through mitochondrial DNA.

Mitochondria DNA are inherited from the mother only. Other maternal relatives also carry the mtDNA; the success rate is about 80%. Both shaft and roots can be used for the extraction and amplification of mt DNA and a final comparison of the mtDNA profiles. However, it does not provide individual specificity.

If the nuclear material is not available for n DNA analysis, mtDNA analysis is done in all cases. It is done after the microscopic examination, as DNA analyses are destructive.

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