Hair specimens are
prepared for microscopic examination by mounting them onto a drop of solvent
(water or alcohol) directly onto a clean microscope slide then covered with a
cover slip (see figure 23 below) in order to visualize the internal microscopic
characteristics.
It may be necessary to apply some weight to the cover slip in order to
ensure a thin mount. The thinner the mount, the easier it is to examine the
hairs.
Figure 23. Illustration of Slide Preparation
Pigment: The pigment granules may be absent as in gray hair or may be so dense that they obscure the inner structural detail of the hair specimen. Granule size can range from very fine to coarse. Consideration is given to local distribution of the pigment across the hair shaft (Figure 63), as well as to variations in distribution and density along the shaft from proximal to distal. The granules can be regularly arranged in streaks or clumps, with consideration given to the size, distribution, and density of these groupings.
Figure 63. Photomicrograph of One-Sided Pigment Distribution
Medulla: The structure of the medulla can vary from continuous throughout the center of the hair shaft to fragmentary, or absent altogether. It can be opaque, translucent, vacuolated, or completely amorphous in appearance (Figures 64-68). When the medulla is fragmentary, the cell structures may appear fusiform, or spindle-shaped. The width of the medulla in relation to the overall shaft diameter should be considered.
The medullary index is used to distinguish animal hair from human hair. It is expressed as a ratio of the shaft diameter to the diameter of the medulla (Saferstein, 2004). In animals the medulla will make up more than 1/2 of the total diameter of the hair. In humans the ratio is usually less than 1/3 (Saferstein, 2004) The medulla can be classified as appearing either absent, fragmented, interrupted or continuous (Lane, 1992) (Saferstein, 2004). Most human head hair with the exception of that of the Mongoloid race has no medulla or a fragmented one. People of the Mongoloid race have a continuous medulla.
Most animals have a continuous or interrupted medulla. Hair of animal origin may exhibit specific patterns such as a uni or multiserial ladder (rabbits) or a lattice (Deer) (Saferstein, 2004)( Lane, )1992 The shape of the medulla as well as the pattern is exhibits can be used to determine species, and when human, racial origin (Saferstein, 2004) (Lane, 1992).
The cortex surrounds the medulla as does the wood of a pencil around the lead. Microscopic structures within the cortex such as pigment granules and fusi (air bubbles) are used to compare one hair to another (Saferstein, 2004) (Kubic & Patraco, 2003).
Figure 64. Photomicrograph of Continuous Clear Medulla
Figure 65. Photomicrograph of Continuous Opaque Medulla
Figure 66. Photomicrograph of Wafer Medulla
Figure 67. Photomicrograph of Trace Medulla
Figure 68. Photomicrograph of Bubbly or Cellular Medulla
Cortex: The general appearance of the cortex should be considered. The margins of the elongated cells comprising the cortex may be poorly defined or may be distinct (Figure 69). These cells are prominent, particularly in hairs that have been bleached and have resulted in a straw-like appearance.
Figure 69. Photomicrograph of Coarse Cellular Appearance
Artificial treatment: Bleaching removes pigment from the hair and can give the hair a characteristic yellow cast. The cortical cell margins may become more prominent and cortical fusi may develop. In addition, harsh or repeated treatments can make the hair shaft brittle, and the scales will appear disturbed. Artificial bleaching can be distinguished from solar bleaching by a sharper line of demarcation between the bleached and unbleached regions. To the experienced examiner, dyed hairs possess an unnatural cast or color. In addition, the cuticle will take on the color of the dye (Figure 70). If hair generally grows at the rate of one half-inch per month, the distance can be measured from the root to the line of demarcation of the dyed portion to estimate the time since dyeing. Repeated dyeing or bleaching results in several lines of demarcation. This would serve to further individualize a particular hair specimen.
Figure 70. Photomicrograph of Dyed Human Hair
It may be necessary to make a scale cast of the hair specimen in order to see the scale pattern more clearly, particularly in the identification of some animal hairs. Ogle and Mitosinka (1973) devised a quick and easy method of making a scale cast with the use of clear nail polish. A thin coat is painted on a glass microscope slide. The hair is placed on the slide and allowed to dry. When the surface has dried, the hair is removed to reveal the scale pattern.
The cuticle is like the outer paint of the pencil. The cuticle is used mainly to observe the scale patterns present which indicate species (Saferstein, 2004) (Lane, 1992) (Crocker, 1999) (Kubic & Petraco, 2003) .
Scale patterns are observed by embedding the hair in a liquid medium often clear nail polish and allowing it to set. Once the polish has air dried the hair is removed leaving a cast of the outer scales (Crocker, 1999).
Scale structure is used to determine species. The patterns may be coronal, petal, or umbricate. Umbricate scales are overlapping and exhibit no apparent pattern. Umbricate scales are found in humans (Saferstein, 2004) Petal scales resemble the scale of a reptile and are not found in humans. Coronal scales are symmetrical and overlap one and other. They are not usually found in humans (Cheyko & Petreco, 2003).
| CUTICLE SCALES--Can you name the pattern found in each animal hair below? Observe the scale patterns from various animals from the Brookfield Zoo. (Part 1) and (Part 2) |
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Mosaic
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Pectinate
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Imbricate
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Petal
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Diamond Petal
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Chevron
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| HUMAN CUTICLE SCALES | DOG CUTICLE SCALES |
Human hairs can generally be identified by racial origin, body area, and other comparison characteristics.
Racial Origin
Key characteristics serve as racial indicators. These indicators are
generalities and apply primarily to head hairs. The examiner may encounter hairs
that cannot easily be associated with a particular racial model because of
poorly defined characteristics, limited size, or inconsistent indicators. These
hairs can be identified as apparent racial mixtures or as not classifiable. In
spite of an inability to substantiate race, the hair may still be of value for
comparison purposes. This racial admixture may serve to further individualize
the hair and its source, particularly if the same mixed racial characteristics
are observed in both the questioned and known samples.
Caucasian (Figures 24 and 25)
Figure 24. Photomicrograph of Cross-section of Caucasian Hair
Figure 25. Photomicrograph of Caucasian Head Hair
Negroid (Figures 26 and 27)
Figure 26. Photomicrograph of Cross-section of Negroid Hair
Figure 27. Photomicrograph of Negroid Head Hair
Mongoloid (Figures 28 and 29)
Figure 28. Photomicrograph of Cross-section of Mongoloid Hair
Figure 29. Photomicrograph of Mongoloid Head Hair
Body Area
Certain features of individual hairs identify the region of the body where it
originated. The features listed are generalities and align themselves with
racial models derived from known samples. Body area can be made with
considerable accuracy; however, variations occur that can make this
determination difficult. Hairs that fall into this category include those that
are immature, transitional, and fragmentary.
Head Hairs
Pubic Hairs