What is this a photo of? What is in the center of the circle? Why are there gradients in color?
Section of a haversian system, or osteon. Note the alternation of clear and dark circles resulting from the alternation in the direction of the collagen fibers (head to toe formation). The type I collagen fibers appear bright when cut longitudinally and dark when cross-sectioned. Inthe center of the osteon is a channel. PSP stain.