Clinical chemistry the denser blood cells and platelets to the bottom of the centrifuge tube, leaving the liquid serum fraction resting above the packed cells. This initial step before analysis has recently been included in instruments that operate on the "integrated system" principle. Plasma is in essence the same as serum, but is obtained by centrifuging the blood "without" clotting. Plasma is obtained by centrifugation "before" clotting occurs. The type of test required dictates what type of sample is used. A large medical laboratory will accept samples for up to about 700 different kinds of tests. Even the largest of laboratories rarely
Sweat gland except the lips, ear canal, prepuce, glans penis, labia minora, and clitoris. They are ten times smaller than apocrine sweat glands, do not extend as deeply into the dermis, and excrete directly onto the surface of the skin. The proportion of eccrine glands decreases with age. The clear secretion produced by eccrine sweat glands is termed sweat or "sensible perspiration". Sweat is mostly water, but it does contain some electrolytes, since it is derived from blood plasma. The presence of sodium chloride gives sweat a salty taste. The total volume of sweat produced depends on the number of functional glands