The theory that ascribes personality characteristics to the effects of bodily fluids, or “humors.”The humoral theory is the oldest known typology, or descriptive system, used for classifying all individuals into a limited number of categories. It was originated in about 400 B.C. by Hippocrates, who believed that a predominance of blood was associated with a sanguine (hopeful) character or temperament,black bile with a melancholic (sad) temperament, yellow bile with acholeric (irritable) temperament, and phlegm with a phlegmatic (apathetic) temperament. If, however, all the humors were mixed in proper proportions, they would produce a well-balanced person. Since the Greeks held that man is a mirror of the whole of nature, many of them believed that the four humors corresponded to the four cosmic elements, fire, earth, air, and water, which Empedocles had postulated in about 450 B.C.As Bromberg (1959) states, “The Hippocratic theory of the four humours, under the dogmatic espousal of Galen, became the guide for all physicians until the Renaissance.” Its nearest counterpart in modern science is the view that the hormones are the basis of temperament. There is evidence that , the size of glands may differ greatly even among normal individuals, so that thyroid or adrenal tissue in one person may actually weigh three times as much as in another. There is further evidence on this point in studies which indicate that some individuals react with typically sympathetic and others with typically parasympathetic responses to the same situations, and that autonomic responses in the same children tend to be stable over a long period (Wenger and Wellington, 1943).Some investigators believe they have found a relationship between these autonomic response patterns and personality measurements (Lacey, Bateman, and Van Lehn, 1952), but others have pointed out that these constitutional patterns—granted that they exist—are not the key to the entire personality structure, since acquired habits, attitudes, and reactions must also be taken into account. Moreover, accurate measurement of autonomic functioning has not resulted in the isolation of a few specific types, as the humoral theory suggests, but shows continuous gradations instead.