CHAPTER XXI. 



PROCESSES INFERRED FROM INDIRECT OBSERVATION: 

 MEMORY AND SLEEP. 



MEMORY. 



THE most prominent characteristic of the Nervous System is the 

 facilitation of its functions which their performance brings about. 

 A mental task which is at first difficult becomes easy by frequent repe- 

 tition; an act which may be performed under the guidance of the 

 central nervous system at first only with effort and concentration of 

 the will and attention, becomes by repetition a habit or even a reflex 

 which is performed almost automatically and without any conscious 

 expenditure of effort. 



Secondary and subsequent to this phenomenon of facilitation is the 

 phenomenon of Fatigue. For example, in the learning of a long passage 

 by rote, as one tries to recall it after the first repetition, recollection is 

 distinctly difficult. With a second repetition recollection is easier, 

 with a third it is easier still and so the progressive facilitation accumu- 

 lates until it becomes possible to repeat a long passage from "Memory," 

 faultlessly and fluently. If, however, the repetitions be still continued 

 or fresh matter added to the lesson a new phenomenon supervenes 

 which is the reverse of that initially experienced. The passage which a 

 little while before was repeated faultlessly cannot now be repeated 

 without mistakes. The attention wanders readily. Recollection 

 becomes increasingly difficult, the consciousness has to be "flogged' ' 

 into activity and finally excessive fatigue compels desistance from the 

 task. The effects of the initial facilitation have not been undone, 

 however, for a return to the task after an adequate interval for recuper- 

 ation reveals the fact that the previous study has implanted memories 

 which disappear from the field of consciousness in many instances 

 only after a lapse of time comparable with the duration of life itself. 



We meet, therefore, in the exercise of any given intellectual function, 

 with two apparently contradictory facts. Performance facilitates the 

 exercise of the function, and it likewise depresses the exercise of the 

 function. We note, furthermore, that the facilitation and depression 

 become evident at different periods of time, the former in the earlier 

 stages of performance and the latter in its later stages. 



Many hypotheses have been advanced by philosophers, psychologists 

 and physiologists in the endeavor to imagine a mechanism which could 

 account for the phenomenon of memory. The vast majority of the 

 mechanistic hypotheses, which are the only ones of which we need 



