SECTION XVII 



THE FUNCTIONS OF THE CEREBRAL 

 HEMISPHERES 



IN an animal possessing cerebral hemispheres it is impossible to foretell 

 with certainty what particular reaction may be evoked by any stimulus. 

 The animal which has been deprived of its hemispheres can, as we have 

 seen, be played on at will, whereas the intact animal is an individual whose 

 actions to judge by our own experience are guided by intelligence, and 

 influenced by motives or by feelings of fear, hunger, pain, and the like. In 

 short, its behaviour is analogous to that which in man we associate with 

 conscious feeling and volition. This association of the volitional manifesta- 

 tions with the cerebral hemispheres has long been assumed, and is borne out 

 by the exact parallelism existing between the degree of intelligence with 

 which an animal is endowed and the extent of development of its cerebral 

 hemispheres. Moreover in man himself there is a proportionality between 

 the average size of the brain, i.e. of the cerebral hemispheres, and the 

 average intelligence of the race. 



Earlier attempts to analyse the factors entering into the sphere of 

 consciousness and to associate with these factors localised parts of the 

 brain failed, largely on account of a faulty psychological analysis and the 

 absence of any proper experimental groundwork for the conclusions put 

 forward. Gall, the founder of phrenology, recognised more clearly than 

 previous authors that the cerebral hemispheres must be regarded as the 

 material basis of consciousness. Impressed, however, by the fact that there 

 .was no proportionality between the acuteness of the senses and the degree 

 of development of the cerebral hemispheres, he considered that any division 

 of functions among different parts of the hemispheres must relate to highly 

 complex psychical conditions, and therefore on very slender grounds allotted 

 to parts of the brain functions such as those of intelligence, memory, judg- 

 ment, amativeness, and so on. These conclusions of Gall were overthrown 

 by Flourens on both theoretical and experimental grounds. In the first 

 place, Flourens pointed out that the mental faculty of man cannot be divided 

 up into a number of different independent qualities or faculties, such as those 

 proposed by Gall. In the second place, he showed that in the pigeon 

 although loss of the whole cerebral hemispheres destroyed intelligence and, 

 associative memory with the actions founded on such endowments, removal 

 of portions of the brain caused simply a lowering of these functions, and it 



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