Page 11 - Strands of Evidence Hair And Fiber

also be used as a mounting medium to provide a human or animal. The medulla of a human hair
second, quick method to observe surface scales of is poorly defined, broken, or even absent, while
hair. Lastly, clear nail polish may be painted onto a animal medullas are well defined and continuous.
microscope slide and used in a similar way to the
Polaroid film-coater. Once the hair has set in the Forensic scientists have developed a statistic called
medium and the polish has dried, the hair can be the medullary index that can be used to determine
removed, and the scale pattern from the cuticle will if a hair is of human or animal origin. The medullary
remain in the cast. index is calculated by measuring the width of the
medulla and dividing it by the total diameter of the
The cortex layer of the hair shaft is the main body of hair shaft. Usually, human hairs have a medullary
the hair and is made of elongated, spindle-shaped width that is less than one-third of the diameter
(fusiform) cells. Additional identifiers, such as of the hair (approximately 0.3), while animal hairs
pigment granules (small, dark, solid structures), have larger medulla and medullary indices greater
ovoid bodies (solid, spherical structures), or irregular than 0.5, indicating that the medulla is at least half
airspaces (cortical fusi), may also be observed. as wide as the total diameter of the hair shaft. In
certain instances, these medullary indices may
The medulla, the central core of the hair shaft, even be used to differentiate between species of
often indicates whether a hair was shed from a animals.

THE MYSTERY OF LYLE AND LOUISE 11