Chap. XXIV.] PRINCIPAL PARTS OF THE BRAIN. 491 



to be called into simultaneous and harmonious activity in 

 Perception, Emotion, Thought, and Volition, evidence is 

 not altogether wanting to show that they are capable of 

 working more or less independently — either {a) where 

 both hemispheres exist, and there is a supposed lack of 

 harmony, with resulting ' double Consciousness ' ; or (h) 

 in the more positive and definite cases in which there has 

 been no impairment of Sense or Intellect noted, although 

 the greater portion of one Cerebral Hemisphere may have 

 been destroyed. On each of these subjects a few words 

 may be said. 



(a.) The evidence in favour of the possibility of a 

 separate and dissimilar, though simultaneous, activity 

 of the two Hemispheres of the Brain is of a very doubt- 

 ful nature, though there are facts familiar enough to 

 physicians which have been thought to support this 

 notion. 



The question was, for instance, raised by Sir Henry Holland* in 

 1840, — " Whether some of the aberrations of mind, which come 

 under the name of insanity, are not due to incongruous action of 

 this double structure [the two hemispheres], to which perfect unity 

 of action belongs in the healthy state ? " He adds : — " The sub- 

 ject is very obscure, and all proof of difficult attainment; but I 

 think it more probable than otherwise that such inequality may be 

 a cause of some among the many forms of mental derangement. 

 . . . . It has been a familiar remark that in certain states of 

 mental derangement, as well as in some cases of hysteria which 

 border closely upon it, there appear, as it were, two minds ; one 

 tending to correct by more just perceptions, feelings, and volitions, 

 the aberrations of the other ; and the relative power of the two 

 influences varying at different times. . . . It is remarkable 

 how distinct an expression to this effect may occasionally be had 

 from patients themselves. I have recently seen a case of which 

 the most marked feature was a frequent and sudden outbreak of 

 passion upon subjects, partly real, partly delusive, but generally 



* " Medical Notes and Reflections," •2ud Ed., 1840, p. 172. 



