72 2 THE POPULAR SCIENCE MONTHLY. 



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 ena- 

 ble 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 re- 

 sults 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 im- 

 pulse 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 pri- 

 marily 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 pos- 

 sible 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 rec- 

 ognized, and conveyed no more idea to him than Chinese charac- 

 acters would 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 fin- 

 ish 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 



