iv CEREBRAL LOCALISATION 193 



anatomy, have long ago made known the localisation of 

 elementary functions in the brain as a fact beyond dispute, 

 but, for instance, to the fact that the faculty of speech, 

 which was obviously acquired through the relations of men 

 to one another, according to pathological evidence has its 

 seat in a definite part of the human brain, in the left temporal 

 lobe. Loss of the power of speech, aphasia, may temporarily 

 occur as a consequence of excessive mental exertion. I have 

 myself experienced this fact, and know that in this condition 

 the power to speak is lost, but not the ability to produce 

 sound. One is only unable to find and to utter words ; one 

 is perfectly conscious of this and is astonished that it is so, 

 and makes vain endeavours to overcome it. 



I consider as a similar condition of less degree another 

 which I have often observed in myself during great mental 

 fatigue, and which friends have told me they also have 

 experienced, namely, that in writing one repeatedly omits 

 letters from a word, or puts wrong letters instead of the 

 right. 



It is universally known that in great mental fatigue one 

 often " forgets " the commonest names, and I have already 

 made the observation on my self that this especially occurs when, 

 as for example in systematic natural history, one has worked 

 at names too much ; the part of the brain which is concerned 

 with such matters is then exhausted and fatigued. 



The following highly peculiar case which seems to me to 

 prove the fact that very complicated faculties, the acquirements 

 of civilisation, are connected with definite parts of the brain, I 

 was able to observe accurately within the last few months : 



A young man who was a connection of mine, and who 

 was a student here in Tubingen, began to require an unusual 

 amount of sleep. As the consequence of this was that he 

 usually did not get up till near mid -day, it was at first 

 attributed to causes which seemed very natural to irregular 

 o 



