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Acicular Crystals
Crystals that are needle-shaped, often slender with sharp points.
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Aggregate
A mass or body of similar particles somewhat loosely associated with one another. See also conglomerate.
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Amorphous Medulla
A medulla that has no distinct form, pattern, or shape when viewed with a transmitted light microscope.
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Anagen
The active growth phase of a hair follicle in the hair growth cycle. The root from a pulled anagen hair is elongated, may be covered with a root sheath, and is usually fully pigmented.
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Anisotropic
(an-: not; iso-: same; -tropos: velocity)
Refers to substances that have more than one refractive index, such as crystals in the hexagonal or tetragonal system (two principal refractive indices), orthorhombic, monoclinic, or triclinic system (three principal refractive indices), oriented polymers, or isotropic substances that are mechanically or thermally strained. Anisotropic substances can be seen between fully-crossed polarizers, if they are not in an extinction position. Compare Isotropic |
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Aplanatic
Free from or corrected for spherical aberration.
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Aramid
Aramid fibers are a class of heat-resistant and strong synthetic fibers. The Federal Trade Commission defines an Aramid fiber as, "A manufactured fiber in which the fiberforming substance is a long-chain synthetic polyamide in which at least 85% of the amide (-CO-NH-) linkages are attached directly between two aromatic rings."
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Arillus
A specialized outgrowth or fleshy covering that is formed from the attachment point of the seed. May also be the thickening of the coat covering the seed of a flowering plant. |
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Becke Line
A band or halo of light (due to diffraction/refraction) seen at the periphery of a specimen when the refractive indices of the specimen and its mounting medium are different; it is used to determine refractive index. In practice, the Becke Line is produced by reducing the numerical aperture of the substage condenser, and focusing above and below the plane of best focus; the Becke Line always moves toward the material of higher refractive index on focusing above the plane of best focus. (Named after the Austrian geologist, mineralogist, and petrologist, Friedrich Johann Karl Becke, 1855-1931, who devised the method).
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Birefringence
The numerical difference between the maximum and minimum refractive indices of anisotropic substances: ε-ω; nII-n┴; γ-α. Birefringence may also be determined by use of compensators, or estimated through use of the Michel-Lévy Interference Color Chart. Birefringence may be qualitatively expressed as low (0 - 0.010), moderate (0.010 – 0.050), or high (>0.050); often birefringence >0.2 is termed “extreme”. “Strain birefringence” is a term used to refer to isotropic substances which exhibit uneven (usually) or spotty birefringence induced by mechanical, thermal, chemical, or other means.
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Bleaching
A chemical or a natural process used to make a hair colorless or lighter than its natural color.
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Buckling
An abrupt change in the shape and orientation of a hair shaft with or without a slight twist, often seen in pubic hairs.
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Catagen
The transitional phase of the hair follicle from the active growth phase (anagen) to the resting growth phase (telogen) in the hair growth cycle.
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Caucasoid
An anthropological term designating one of the major groups of human beings originating from Europe and from the Indian sub-continent.
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Cleavage
The quality or property of a crystallized substance, mineral, or rock of splitting, parting, or separating along definite planes. Classic examples include the minerals calcite and gypsum.
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Columnar
A term used to describe a shape resembling tall, narrow, somewhat cylindrical or prismatic crystals. In some traditional texts, the term is applied to aggregates.
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Compensator
A device with known, fixed or variable retardation, and vibration direction, used for determining the amount of retardation (hence, the thickness and birefringence) of an anisotropic substance. It is also used to determine the sign of elongation of elongated anisotropic specimens. The most common compensator is the first-order red (530-550 nm retardation), but other compensators frequently used include the quartz wedge (1-6 orders), the Berek (1-3, 1-5, 1-30 orders), the quarter-wave (~137 - 147 nm), and the Sénarmont. Compensators are typically introduced into the light path through a bodytube slot between the objective and the eyepiece.
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Conglomerate
A mass or body of dissimilar particles somewhat loosely associated with one another. See also aggregate.
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Continuous medulla
A medullary appearance showing no disruptions along the shaft of the hair.
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Convolution
A rotation or twisting of the hair shaft that can occur naturally, from disease, or as a result of mechanical force.
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Cortex
The primary anatomical region of a hair between the cuticle region and the medullary region composed of elongated and fusiform cells.
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Cortical fusi
Small spaces that appear as tiny dark structures within the hair shaft; they can be filled with air or liquid.
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Cortical texture
The relief or definition of the margins of the cortical cells as viewed using transmitted light microscopy.
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Cracked cuticle
A cuticle with linear breaks that are perpendicular to the length of the shaft.
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Cubic System
See Isometric
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