among whom Charcot, Nothnagel, and Ferrier must be named, that the same statement may be made with regard to the brain of man. To-day a practical application is being constantly made in our hospitals of these important discoveries. For they not only enable us to determine the position of disease in the brain, but also afford a guide to the surgeon, who can cut through an apparently healthy head and skull and remove the diseased tissue. The results of brain surgery form one of the triumphs of medical science of which physiologists may justly take the credit. It is now well determined that from the eye, or from the ear, or from the skin definite nerve tracts can be traced to special regions of the brain. It is well known that all impressions received by the eye, or ear, or skin set up impulses which traverse these tracts and reach these special areas of the brain surface or cortex. When an impulse reaches the cortex a conscious perception is produced, and of this perception a definite memory remains, which memory is necessarily connected with the brain cells in the special area primarily excited. If disease destroys a sensory area, perceptions are no longer possible in the sensory organ to which it belongs, and memories stored up in that area are permanently lost. From this loss of particular perceptive power and of memories it is possible to determine the position of disease in the brain so exactly that it has been found feasible and justifiable to proceed to the removal of the disease, such as a clot or tumor, producing the symptoms.
It would afford material for an entire paper to study defects of memory and to describe some of the curiosities of thinking which result from such defects. A few examples may be related.
I saw lately a business man of keen mind and good general memory, who was not paralyzed in any way, and was perfectly able to understand and to talk, but who had suddenly lost a part of his power of reading and of mathematical calculation. The letters d, g, q, x, and y, though seen perfectly, were no longer recognized, and conveyed no more idea to him than Chinesewould to us. He had great difficulty in reading—had to spell out all words, and could not read words containing three letters. He could write the letters which he could read, but could not write the five letters mentioned. He could read and write some numbers, but G, 7, and 8 had been lost to him; and when asked to write them his only result, after many attempts, was to begin to write the word six, seven, or eight, not being able to finish these, as the first and last contained letters (x and g) which he did not know. He could not add 7 and 5 together, or any two numbers of which 6, 7, or 8 formed a part, for he could not call them to his mind. Other numbers he knew well. He could no longer tell time by the watch. For a week after the onset of the