The Pineal Gland

mied nearly in tbe center of the B brain in any mammal is a small white structure, sbaped somewhat like a pinecone, called tbe pineal body. ln man this organ is rougbly a quarter of an inch long and weighs about a tenth of a gram. The function of tbe pineal body has never been clearly understood. Now that tbe role of tbe tbymus gland in establishing tbe body’s immunological defenses bas been demonstrated, the pineal bas become perhaps the kst great mystery in tbe pbydology of mammalian organs. Tbis mystery may be nearing a solution: studies conducted witbin tbe past few years indicate that tbe pineal is an intricate and sensitive “biological clock,” converting cyclic nervous activity generated by light in tbe environment into endocrine-&at is, bormonal-infonnat&n. It is not yet certain what pbysiobgical~dependontbepineal clock for cues, but tbe evidence at band ~ggest.9 that the pineal participates in sanewayintbequlationoftbegonads,orsexglands.