Serum
in anatomy, a pale yellowish liquid obtained by drawing blood from the vessels and allowing it to separate into a thicker and a thinner portion. The thinner one is the serum. It consists of proteid substances, fats, extractives, and saline matter. The solid contents of the serum is 9.22 in males, and 8.29 in females; the rest is water. There is also a serum of chyle and one of lymph. In chemistry, the opalescent liquid, containing milk-sugar and various salts, which separates when milk is curdled by the action of acids, rennet, etc.