This is a photograph of the prepared "Common Goat" slide from the Cargille Hair Standard set. The plane of focus is on the
center of the part of the hair filled with mounting medium so that the detail of the medulla structure is visible.
Transmitted Crossed Linear Polarized Light
Significance in the Environment:
Wool has a refractive index along its length of about 1.56 and perpendicular to its length of about 1.55.
It has a birefringence of about 0.01 and a positive sign of elongation.
Von Bergen, Werner, WOOL HANDBOOK: VOLUME ONE, Interscience Publishers, pp. 364-365, 1963