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DUAL CONSCIOUSNESS. 



RATHER more than two years ago I considered in the pages 

 of * Science Byways ' the theory originally propounded by 

 Sir Henry Holland, but then recently advocated by Dr. 

 Brown- Sequard, of New York, that we have two brains, 

 each perfectly sufficient for the full performance of mental 

 functions. I did not for my own part either advocate or 

 oppose that theory, but simply considered the facts which 

 had been urged in support of it, or which then occurred to 

 me as bearing upon it, whether for or against. I showed, 

 however, that some classes of phenomena which had been 

 quoted in support of the theory seemed in reality opposed 

 to it, when all the circumstances were considered. For ex- 

 ample, Brown-Sequard had referred to some of those well- 

 known cases in which during severe illness a language 

 forgotten in the patient's ordinary condition had been re- 

 called, the recollection of the language enduring only while 

 the illness lasted. I pointed to a case in which there had 

 not been two mental conditions only, as indicated by the 

 language of the patient, but three ; the person in question 

 having in the beginning of his illness spoken English only, 

 in the middle of his illness French only, and on the day of 

 his death Italian only (the language of his childhood). The 

 interpretation of that case, and of others of a similar kind, 

 must, I remarked, be very different from that which Brown- 

 Sequard assigned, perhaps correctly, 'to cases of twofold 

 mental life.' A case of the last-named kind has recently 

 been discussed in scientific circles, which seems to me to 



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