contributory role in manic-depressive reactions. They do not, however, agree on the relative weight to be assigned to heredity, constitution, and organic pathology. Statistical studies by Slater (1944) and Kallmann (1952, 1953) indicate that between 15 and 25 per cent of manic-depressives have close relatives who are affected with the same disorder. In addition, Kallmann (1958) has found a concordance rate (if one has it the other gets it) of 26.5 per cent between fraternal twins and 95.7 per cent between identical twins. All these figures may be compared with an expectancy of .5 per cent for the general population. He also noted that schizophrenic and manic-depressive reactions do not both occur in the same twin pair, and concluded that the manic-depressive condition is due to a genetic defect in the neuro-hormonal mechanisms that control emotion. These studies are strong evidence for hereditary predisposition, but they do not rule out environmental factors such as disturbing experiences and parental attitudes operating early in life.Other investigators have found strong evidence of extreme mood swings during childhood, and have concluded that they arise out of a “cyclothymic” constitution. This tendency has not been traced to any specific physiological make-up, and it is not known whether it is a hereditary predisposition, a constitutional tendency acquired in the course of early growth, or a learned behavior pattern. There is also a possibility that the mood swings are related to specific physiques. Kretschmer (1925) found that manic-depressives tend to be short, stocky, and vigorous, while Sheldon et al. (1954) observed that they may be either mesomorphic (muscular, energetic) or endomorphic (plump, extroversive) individuals. Other studies have shown that manic-depressive reactions are not confined to these personality types. Moreover, it is not known whether the physique fosters the temperamental patterns or the other way around. There may well be an interaction between the two factors. See CONSTITUTIONAL TYPES.The question of organic pathology in manic-depressive reactions is under active investigation. So far no underlying structural or toxic condition has been demonstrated, and no clear-cut brain wave abnormalities have been found in recovered patients. On the other hand, there are indications that the reaction patterns themselves produce, or at least are associated with, abnormal brain functions. Different investigators have found hypoactivity of certain motor areas in depressed patients. Some have noted excessive excitation, overloading, and weakened inhibition of higher centers in manic states, and inhibition of lower centers in depressive states. Others have found distinctive biochemical changes in brain functioning in each state. All these phenomena may be the result rather than the cause of this disorder, although they may also feed back into it. Psychological factors have been receiving increasing attention in recentyears. Even where hereditary and constitutional tendencies exist, family background, life situation, and precipitating stresses may play an essential role in producing the actual illness. There is some evidence that both manics and depressives come from “oversocialized” homes where competitiveness, envy, and the search for social approval set the pattern. In one extensive investigation, disturbing life situations were found in at least 80 per cent of patients. Another study revealed typical precipitating stresses of three kinds: death of a cherished significant person; failure in an important personal relationship; and a severe disappointment or setback in work life. All three have the common denominator of great personal loss, and represent loss of meaning and emotional security.Specific factors have been found to be operative in predominantly manic and predominantly depressive patients. Prior to their illness, manic patients have usually been ambitious, energetic, outgoing individuals who place a high value on achievement and conformity. Although they appear confident, they are basically overdependent; and in spite of their sociability they are often envious and hostile. They react to stress by a “flight into reality”—that is, restless activity rather than withdrawal. In the fully developed psychosis, they unconsciously attempt to deny their failures or inadequacies, and allay their anxiety and bolster their ego by proposing important projects, meddling in other people’s affairs, and keeping themselves occupied every minute of the day. This, process may develop to a point where both the sensory and motor systems become so overloaded that the patient becomes incoherent, wild, and finally exhausted. Many authorities believe these activities are primarily a means of warding off depression, and analytically oriented therapists suggest that in the manic stage the patient is identifying with the dominant, aggresive parent, usually the father. See FLIGHT INTO REALITY.Depressed patients share the manic’s conventionality and concern for the opinions of others, but tend to be meticulous, perfectionistic, anxious people who frequently belittle and reproach themselves. They have a rigid, overdeveloped conscience which makes them susceptible to strong guilt feelings and unable to express hostile impulses. As a result of these tendencies they react to disappointment, failure, or loss of loved ones by turning their anger and resentment inward. They proceed to blame themselves for their difficulties, discover that they have committed or wanted to commit a “sin” (usually trivial or irrelevant) in the past, and feel increasingly worthless.Psychoanalysts and others have put particular emphasis on the death of a parent as a precipitating factor in this disorder, and believe that repressed hostility toward that person is the major cause of the feelings of guilt and depression. The hostility may in some cases be due to the fact that the parent placed the burden of maintaining the family’s prestige on the patient. The guilt feeling may be so strong that the patient may come to believe that his own hostile feelings were responsible for the parent’s death.Recent studies have emphasized the idea that the loss of a loved one, or some other drastic change, may produce depression by depriving life of meaning. This may happen to a wife who has been discarded in favor of a younger woman, to a man who has lost or been retired from an occupation on which his whole existence has been centered, or to individuals who lose a friend on whom they have long been dependent. These cases, too, are usually aggravated by feelings of failure or guilt, and the patient may unconsciously seek to relieve his suffering by slowing down painful thought processes or by denying himself every satisfactionof life as a means of atoning for fancied shortcomings. In some cases, the patient becomes not only depressed but agitated, and in others he tries to put an end to a life that seems bereft of all meaning and hope.Most investigators agree that biological factors of one kind or another play at least a