AMNESIA, or loss of memory, may vary in degree from the occasional failure to remember which is allowed as normal, to the absolute extinction of all mental impressions or pictures. This word and the expression memory are here used in a restricted sense, reference being had only to purely intellectual and sensorial acts related to intellection. If we take the general or biological sense of the term memory as meaning the retention of all kinds of residua from centripetal impressions and of motor {29} centrifugal impulses, including common sensory and visual impressions, special sense impressions, all unconsciously received impressions, emotional, intellectual, and motor residua, we should consider amnesia in a correspondingly general way. This, however proper for a physiological study, would be far too complex and premature for an introduction to practical medicine. Recognizing memory, therefore, as a universal organic attribute—a capacity to retain impressions—we will treat of it only in the commonly-accepted sense referred to supra. Failure of memory may be real or apparent. In the latter sense amnesia is induced by diversion of the attention into a channel different from that in which the line of inquiry is conducted. A normal example of this is seen in the state known as preoccupation, where a person intent upon a certain thought or action forgets who is about him, where he is, and if asked questions fails to answer or answers incorrectly. In pathological states, as in acute curable insanity, apparent loss of memory is often caused by the domination of an emotion or of delusions. In both cases, if the subject can be roused or brought to himself, he remembers all that we inquire about and is amused at his previous false answers or silence. Real amnesia consists in the actual blotting out of recollections or residua in a partial or general manner, for a time or permanently. These differences serve as the basis of a complicated subdivision of amnesia which it is not necessary to fully reproduce here. Temporary partial amnesia is a variety which is frequently observed in normal persons, even the most gifted. A word or fact escapes us, seems wholly lost for a few minutes, hours, or days; the more we strive to recall it, the less we succeed; yet later, when not sought for, the fact or word appears in our consciousness as if spontaneously, but more probably by some effect of the law of association. Such partial and momentary forgetfulness may assume proportions which render it pathological. What is known as transitory aphasia may be classed in this group. In a few minutes or hours a person without apoplectic, epileptic, or paralytic phenomena loses all power to express his thoughts by speaking or writing; there is verbal amnesia and agraphia. The subject is conscious of his condition and of the wholly futile or incorrect attempts he makes to communicate with others.