958 Dynamic Theory. 



There are many cases on record in which one side of the brain has 

 become so diseased as almost to destroy it, without producing any ver} r 

 noticeable deficiency in mental action. It follows, in such a case, that 

 all the mental functions are assumed and carried on by the sound hemi- 

 sphere. If one eye or ear is injured, we can still see or hear with the 

 remaining organ ; and there can be no doubt that one hemisphere alone, 

 if properly educated, is able to carry on all the functions of mentality ; 

 and there is reason to believe that in most individuals one hemisphere 

 actually does the greater part of the work. Again, a sudden injury to 

 one hemisphere, even when apparently slight, may produce very serious 

 results, while a chronic disease, which produces a much greater displace- 

 ment, may extend so gradually that tliQ uninjured parts may have time 

 to take up the functions abandoned by the diseased portions, so that 

 little or no functional disorder is exhibited. 



Some years ago, Dr. Brown-Sequard, advancing the idea that most 

 of .our work is done with a half brain, proposed a system of education 

 which should bring both halves into active use, and claimed if this were 

 done, our mental powers would be nearly doubled. This theory might 

 be tested to some extent by observing whether ambidextrous people are 

 smarter than others. 



In chapter 73, examples under the head of abstraction, &c. , were 

 given, showing a considerable part of the cerebral activity concentrated 

 upon a single line of thought engrossing the attention, while all the 

 cerebrum not thus engaged lay in a dormant condition, so that it could 

 not be fully aroused by an ordinary sensory stimulation. The absurd 

 replies given in such cases, showed nothing but unconscious reflex cere- 

 bral action ; as a sleeping boy will mechanically and unconsciously say 

 "yes" when ordered to wake up, and yet sleep on. It was pointed 

 out that these states of abstraction are simply more pronounced condi- 

 tions of ordinary attention, and that our ordinary daily experience in- 

 volves the division of the cerebrum into two parts, an active and a pas- 

 sive one. The active one absorbs the attention, conscious or uncon- 

 scious, l while the other is in an unconscious and quiescent state. The 

 active portion is generally much the smaller, consisting of only a few 

 organs at a tinte, and not exactly the same for any long time in succes- 

 sion, except in cases where a person is occupied upon a narrow line of 

 work of long continuance. There is a more or less complete severance 

 between the active and the inactive part, and the latter being deprived 

 of attention, and the power to act, is said to be "inhibited." In ordi- 

 nary states, the line between the active and the inhibited organs is shal- 

 low and wavering, but in the more intense states it becomes more defi- 



1 As explained elsewhere, the essential part of attention is its power of directing the 

 now of the blood to wasting parts. When the parts are wasted in unconsciousness, this 

 directive agency remains in action unconsciously, which accounts for its apparently 

 paradoxical designation. 



