A chronic degenerative disease of the central nervous system, usually occurring between the ages of fifty and seventy. Atrophy takes place primarily in the thalamus, basal ganglia, and reticulating activating system, all of which are concerned with motor control.Initial symptoms are usually rigidity and tremor in the muscles of one arm, gradually spreading to the leg on the same side of the body, then to the neck and face, and finally to the limbs on the other side. In time the face becomes masklike, speech grows halting and indistinct, and there is usually a tendency to lean stiffly forward and walk at a half run. This is called a “festinating gait,” a term derived from an archaic word for “hurry.” There is little or no effect on intelligence, but the patient may develop psychological symptoms which result from his reaction to the disease. These usually include apathy and inactivity, social withdrawal, and inability to concentrate and maintain intellectual interest. There are an estimated half million cases of Parkinson’s in this country. The cause of the disease is unknown, although one type is associated with arteriosclerosis. Spellman (1962) has found indications of inherited metabolic defects in a small percentage of cases, but most studies of the disease point toward an acquired deficiency in brain metabolism, possibly caused by a virus that attacks nerve cells leading to the motor cortex. Parkinsonian symptoms may also result from epidemic encephalitis, carbon monoxide poisoning, and brain tumors.No treatment yet devised is completely effective. Early detection, however, is essential, since antispasmodic and muscle relaxant drugs can be used to relieve rigidity and tremors, and psychotherapy is often effective in controlling the psychological reactions. Recently surgical methods have been developed which have been successful in arresting the progress of the disorder in about 90 per cent of the cases. In one technique, defective cells in the thalamus (which switches impulses to the brain’s motor centers) are destroyed by carefully dripping a freezing solution into the affected area (cryosurgery).