It is commonly stated that a most important cause of the disease is the general malnutrition incident to age. Since only a small proportion of the aged develop dementia, this is probably only a cooperating factor. Other causes mentioned are overwork, emotional strain, traumatisms, intoxications (especially alcoholism), cerebral arteriosclerosis and perhaps heredity. =Pathologic Anatomy.=—The disease is organic, the brain exhibiting definite pathological tissue changes. There is an atrophy of many nerve cells and a proliferation of neuroglia fibers, so that the cerebrum becomes shrunken and hard, with thickened meninges and thinned cortex, and shows a loss of weight. The cerebral arteries may or may not exhibit sclerosis, thrombosis, or miliary aneurisms, with resultant areas of softening. The cells show pigmentary degeneration and many of the association fibers have disappeared. =Onset.=—The onset of this dementia is usually very gradual, the condition not being recognized until rather marked. It occurs mainly in the seventies and later and in the late sixties, being rare before sixty. It often follows financial reverses, emotional shock, or various diseases. The earliest symptoms are a change in the person’s disposition, slight disorders of memory, and trivial lapses of various sorts. As the disease progresses the symptoms become more marked and fundamental, involving not only the intellectual but also the emotional and volitional phases of consciousness. Interest in the outside world begins to flag, attention to wander, perception to be incomplete and inaccurate, association of ideas to be slow, memory to weaken and judgment to be impaired. Memory of the most recent incidents is the first to be lost, of recent years next, and then of middle age so that the patient may not recognize his own children or know, for example, that his wife is dead; finally the memory even of youth is lost and the patient is to all intents and purposes a child, his condition being an exaggeration and aggravation of that commonly known as “second childhood.”