In testing a subject's memory due attention should be paid to the law of the survival of older and more interesting residua, as well as to the power of the law of association. Such questions should be asked as pertain to recent events in the patient's experience, and about matters which are not closely related logically. A patient who might tell us nearly all about his early personal experiences, his business and family relations, incidents of his childhood, etc., would fail to remember what he had for breakfast, what he did the day before, etc. The physiological cause of real amnesia is impairment in the vitality (nutrition) of ganglion-cells in the various cerebral sensory areas or centres, and of the motor area as well (motor residua). In cases of transitory amnesia we suppose this to be due to the action of toxic agents, to anæmia, and impaired molecular or chemical nutrition, as after acute diseases, in extreme debility, in psychoses, etc. In cases of terminal permanent dementia, autopsies afford us evidence of degeneration and disappearance of ganglion-cells: we find granular and fatty pigmentation, atrophy, calcarous degeneration of these bodies, thickening and shrinkage of the neuroglia, and degenerative changes in blood-vessels. Doubtless degeneration or destruction of association fasciculi of nerve-fibres in the cortex cerebri or in the white substance plays a considerable part in the production of permanent amnesia, but we are as yet unable to give a clear demonstration of this. Theoretically, we may admit an organic loss of memory with the following conditions of the brain: (1) diseased perceptive (sensory) centres or motor area with normal association fasciculi; (2) normal perceptive centres and motor area with degenerate or broken association fasciculi, connecting these parts with one another and with the more strictly ideational or expressive (centrifugal) areas and parts of the brain and spinal cord. Amnesia—or, more properly speaking, dulness of perception and feebleness of retention of residua—occurs as a strictly congenital condition from imperfect cerebral development, or a little later in life from infantile diseases, constituting one of the aspects of idiocy.