Blood blood clotting in a transparent container. When blood is drawn in a glass container and left undisturbed for about an hour, four different layers can be seen. A dark clot forms at the bottom (the "black bile"). Above the clot is a layer of red blood cells (the "blood"). Above this is a whitish layer of white blood cells (the "phlegm"). The top layer is clear yellow serum (the "yellow bile"). The ABO blood group system was discovered in the year 1900 by Karl Landsteiner. Jan Janský is credited with the first classification of blood into the four types (A,
Eccrine sweat gland duct, the "acrosyringium"; a dermal duct, consisting of a straight and coiled portion; and a secretory tubule, coiled deep in the dermis or hypodermis. The eccrine gland opens out through the sweat pore. The coiled portion is formed by two concentric layer of columnar or cuboidal epithelial cells. The epithelial cells are interposed by the myoepithelial cells. Myoepithelial cells support the secretory epithelial cells. The duct of eccrine gland is formed by two layers of cuboidal epithelial cells. Eccrine glands are active in thermoregulation by providing cooling from water evaporation of sweat secreted by the glands on the body surface