Page:Popular Science Monthly Volume 25.djvu/632

616 recognized them by the sound of their voices. He even forgot his own appearance, and, being in a large public gallery, and seeing, as he supposed, some one in a doorway barring his passage, he stepped forward to ask the stranger to let him pass, when by the motions he realized that it was his own figure seen in a large mirror. This loss of visual memory extended to memories of his childhood as well as to those acquired recently. It interfered much with his power of reading. In reading a book or in adding a column of figures it was necessary for him to have recourse to movements of articulation of his tongue and lips in order to understand what he read or in order to add. While formerly he could remember easily what he read, he now was obliged to read aloud anything he desired to commit to memory, and thus to learn it by impressing his auditory memory. An interesting detail of the affection was the fact that in his dreams he no longer saw objects, but merely heard sounds or words.

Thus he had been deprived entirely of one class of memories, while all others were still at his command. As a consequence, there had come about a complete change in his character, which can easily be understood when one considers how largely one's thinking is made up of the comparison of one set of memories with another, and how frequently the whole circuit of one's thoughts and actions centers about one group of memories. This man was an artist, and in a moment all the powers, the result of long study and labor, which enabled him to perform and enjoy his life-work, were taken away. In this case, as in the first one related, the disease must have been situated in that part of the brain where visual memories are stored, viz., in the posterior part.

Such a loss of visual memories may be temporary, as is well illustrated by the case of a city district messenger-boy, who found on several occasions that he suddenly lost his way and could not recognize streets with which he was usually familiar, so that he was obliged to ask a policeman to take him to his home; where, however, in the course of a few hours he recovered his memory of places and of faces which he had lost. In this case, which may be regarded as one form of epilepsy, the loss of memory can be explained by the hypothesis that a spasm of the arteries occurred in the posterior part of the brain, just as such a spasm in those of the face gives rise to a sudden pallor.

Visual memories are not the only ones to be temporarily or permanently lost. There is another class of cases whose study gives unmistakable evidence of the localization of memories in that part of the brain in which the original perception occurred. It has been stated that the auditory nerve sends a tract to the lower lateral portion of the brain (the temporal region), and that destruction of this region in animals gives rise to deafness. When this part is injured by disease in man, a peculiar condition is observed, known as word-deafness.