ON ACQUIRED PSYCHICAL HABITS. 307 



is the instrument of our bodily activity, shapes itself to the mode in 

 which it is habitually exercised, we seem justined in assuming that 

 the same thing is true of the Cerebrum, which is the instrument of 

 our mental activity. For in no other way does it seem possible to 

 account for the fact of very frequent occurrence, and noticed in a pre- 

 vious paper, that the presence of a Fever-poison in the blood pervert- 

 ing the normal activity of the Cerebrum so as to produce Delirium 

 brings within the " sphere of consciousness " the " traces " of expe- 

 riences long since past, of which, in the ordinary condition, there was 

 no remembrance whatever. 



The same occurrence has been noticed as a consequence of acciden- 

 tal blows on the head ; though these more commonly occasion the 

 loss than the recovery of a language. The following case of this kind 

 is mentioned by Dr. Abercrombie, as having occurred in St. Thomas's 

 Hospital : 



" A man who had been in a state of stupor consequent upon an injury of 

 the head, on his partial recovery spoke a language which nobody in the hospital 

 understood, but which was soon ascertained to be Welsh. It was then discov- 

 ered that he had been thirty years absent from Wales, and that, before the 

 accident, he had entirely forgotten his native language. On his perfect recov- 

 ery, he completely forgot his Welsh again, and recovered the English language." 

 (Op. cit., p. 148.) 



It seems perfectly clear, then, that, under what we cannot but term 

 purely Material conditions, strictly Mental phenomena present them- 

 selves. It is common to the whole series of cases, that the Automatic 

 play of the " Mechanism of Thought " does that which Volition is un- 

 able to effect. Whether it be the toxic condition of the Blood, or the 

 simple excitement of the Cerebral Circulation generally, or the special 

 direction of Blood to a particular part of the Brain, it is beyond our 

 present power to tell ; but, as all Brain-change is (like the action of 

 any other mechanism) the manifestation of Force, the production of 

 these unusual Mental phenomena, by the instrumentality of an unusual 

 reaction between the Blood and the Brain-substance, is no more diffi- 

 cult of comprehension than that of ordinary forms of Psychical ac- 

 tivity, which we have seen reason to regard as the results of the 

 translation (so to speak) of one form of Force into another. 



The intimacy of the relation between the Psychical phenomena 

 of Memory and Physical conditions of the Brain is further shown, by 

 the effect of Fatigue and the impaired Nutrition of Old Age in weak- 

 ening the Memory, and of disease and Injury of the Brain in impair- 

 ing or destroying it. Every one is conscious of the difference in the 

 activity of the reproductive faculty in which Memory consists, accord- 

 ing as his mind is " fresh," or his head feels " tired." The latter state, 

 in which the Automatic activity and the directing power of the Will 

 are alike reduced, is clearly dependent, like the feeling of muscular 

 fatigue, on the deterioration of the Organ, or of the Blood, or of both 



