Unit 9- Hair and Fibers Flashcards
Fibers are considered to be ________ because they are generally _______
class evidence, mass produce
Fibers are used to
create a link between crime scenes and subjects.
Fibers can originate from many different sources:
carpeting, clothing, linens, furniture, insulation, rope/ligature, tape, paper
Two General Types of Fibers:
1) Natural
derived from animal hairs or plants
2) Synthetic
man-made
Natural Fibers: Animal Hairs
Sheep (wool); most common
Goat (mohair and cashmere)
Camel (wool)
Llama
Alpaca (wool)
Fur βibers from mink, rabbit, beaver, etc.
Silk (βiber from the cocoon of the silkworm)
Natural Fibers: Plant Fibers
cotton most common; ribbon-like shape with irregular twists
βlax (linen)
ramie
sisal often used in linen rugs
jute often used in ropes
hemp common name for cannabis for industrial/non-drug use;
typically used for rope or sack
kapok fiber from kapok tree seed pods; used in pillows and
mattress stuffing
coir coconut husks; used in carpet and rugs
Acrylics
> wool-like; soft and warm
quick drying and resistant to moth
Rayon
> cellulose-derived regenerated thin βiber
Acetates
> cellulose-based wrinkle resistant βiber
Nylon
> also common; elastic and strong
lustrous and silk-like when stretched
βirst created by DuPont in 1935
Kevlar
> light, but strong synthetic βiber developed by DuPont in 1965
heat resistant
typically used for bullet-proof vests, military applications, racing
tires, etc.
Nomex
> a variation of Kevlar
βire resistant
used by firemen and disaster response teams
Fiber
> a fine, slender piece of thread or filament
Yarn
> a twisted aggregate of fibers
Textile
> woven fibers; fabric
Weaving
Lengthwise threads (warps) are woven by crosswise threads (wefts) in a repeated pattern.
Plain
> firm; tends to wrinkle
Basket
> not very durable
shrinks when washed
Satin
> not durable
shiny surface
Twill
very strong, dense and compact, but soft
Leno
> open weave
easily distorted
Microscopic Comparisons
> color
diameter
surface markings
delustering agent (TiO2 added to reduce shine)
Polarized Light Microscopy
determines birefringence using polarized light
(difference between two refractive indices)
Fourier Transform Infrared Spectroscopy (FTIR)
analysis of chemical composition based on their ability to absorb light at different wavelengths
UV/Visible Microspectrophotometry
distinguishes slight/subtle color differences based on absorption of light at different wavelengths in the ultraviolet and visible range
Significance of Fiber Evidence
The Questioned fiber could have originated from the known sample.
The Questioned fiber did not originate from the source represented by
the known sample.
The number of fibers is _______ to the likelihood of actual contact (i.e., the greater the number of fibers, the more likely that contact actually occurred).
directly proportional
Hair
a slender threadlike outgrowth from the follicles of the skin of mammals
Keratin
a protein that makes up most of the hair shaft
Pigment (gives hair its color)
- melanin
- pheomelanin (redheads only)
Cortex
the main body of a hair (wooden portion of a pencil)
Medulla
the central cells of the cortex (the lead of a pencil); not always present
cuticle
a layer of scales covering the hair shaft (a layer of yellow paint on a pencil)
proximal end
root
distal end
tip
ovoid bodies
- spheric to oval structure
- mostly found in cattle and dog hairs, but also in some human hairs
cortical fusi
elongated spindle-shaped air spaces in the cortex
anagen phase
- active growth stage
-ribbon like tip - found with follicular tag
catagen phase
intermediate stage of growth
telogen phase
- resting stage
- has a bulb like shape
- often found with very little pigment
- often found with abundance of cortical fusi
hairs that are forcibly removed often end up with a ____ attached to the proximal end
follicular tag
Postmortem root band (dead man’s. root)
a dark band that may appear near the root of the hair originating from a decomposing body
pigments
human: constant color and pigmentation throughout the hair shaft
animal: often seen with radical color changes
medulla
Human: thin and amorphous
Animal: wide, regular, well-defined, repeated patterns
scale structures
Human:
- overlapping imbricate scales
- flattened with narrow margins
Animal:
- imbricate scales
- crown-shaped coronal scales
- petal-shaped spinous scales
caucasian
- moderate shaft diameter with very little variation
- light to moderate pigment density with fairly even distribution
- oval- shaped cross section
mongoloid
- coarse shaft diameter
- streaky pigments with heavy density
- thick cuticle
- round cross-section
negroid
- fine to moderate shaft diameter
- considerable variation throughout the hair shaft with prominent twists curls
- heavy pigment density with aggregate pigment clumpings
- flat cross-section
head hairs
-much longer than other hair types
-soft
- have artificial treatment
pubic hairs
- often coarse in diameter with wide variations
- prominent “buckling”
limb hairs (arm or leg)
- fine diameter with little variation
- arc-like gross appearance
- usually tapered or abraded
facial hairs (beard/mustache)
-very course diameter with irregular or triangular cross-section
- very broad and continuous medulla
- often with double medulla
- stiff texture
chest hairs
- moderate and variable shaft diameter
- tip often dark in color
- long and fine
- arc-like gross appearance
- granular medulla
- stiff
axillary hairs
- less buckling.
- medulla similar to limb hairs
- fine tip
eyebrow and eyelash
stubby and sabber like appearance
fur hair vs guard hair in animals
fur: fine diameter, designed for insulation
guard: coarse diameter, designed for protection
pili annulati
ringed or banded hairs
trichorrhexis nodosa
conspicuous nodes due to immuneodefiency or small bowel disorder
information provided by hair examination
- human or animal
- race
- where in the body
information not provided by hair examanation
age and gender
hair may be used to distinguish identical twins who
cannot be distinguised based on their DNA because of environmental effects
polyester
- wrinkle resistance.
- cotton
