Temporary complete amnesia is almost equivalent to loss of consciousness, yet not strictly so. For example, after a sharp blow upon the head a person may perform complicated acts, reply to questions, and apparently act normally, yet after a variable time he will declare that he remembers absolutely nothing of the injury and what he did or said for hours or days afterward. The same phenomenon is observed in the course of psychoses, neuroses (epilepsy), in some acute diseases, and in certain states of intoxication. Permanent partial amnesia occurs in states of dementia, such as senile dementia, paralytic dementia, and in certain cases of aphasia. Great gaps exist in the patient's memory; some things are well recalled, others wholly and for ever effaced. The psychological law governing the failure of memory in these cases is that the earliest and strongest impressions survive, while recent and less forcible (_i.e._ less interesting) ones are lost. Substantives or names are especially liable to obliteration, as are also many of the delicate residua which lie at the basis of the subject's ethical conceptions and acts. {30} Permanent complete amnesia is observed at the end of degenerative cerebral diseases, as organic dementia, whether of the form termed secondary or that designated as paralytic. Sometimes after acute general diseases the memory may be a perfect blank for a considerable length of time, and education has to be repeated. Memory may be so completely absent that cases are known in which the patient gave a fresh greeting to the asylum physician every two or three minutes indefinitely, as if each were a first meeting. Momentary perception and automatic (reflex) response are there, but no impression is made; there is no residuum left in the cortical centres. In these cases amnesia is accompanied by degeneration of the visual, auditory, etc. cortical areas or centres. An interesting form of amnesia, not generally recognized as such, is the loss of acquired skill in muscular movements, such as are necessary for writing, for using tools, and for doing various delicate professional movements. Here the motor residua acquired by laborious education or training are gradually lost without actual paralysis or ataxia. This variety is exquisitely illustrated by certain cases of dementia paralytica where long before marked intellectual symptoms occur there is loss of skill in mechanical arts and in handwriting.