CHAPTER IX. 



THE GENERAL PHYSIOLOGY OF THE CEREBRUM 

 AND ITS MOTOR FUNCTIONS. 



From the time of Galen in the second century of the Christian 

 era the cerebrum has been recognized as the organ of intelligence 

 and conscious sensations. Galen established this view not only by 

 anatomical dissections, confirming the older work of the Alexandrian 

 school (third century B.C.) in regard to the origin from the brain 

 of the cranial nerves, but also by numerous vivisection experiments 

 upon lower animals. All modern work has confirmed this belief 

 and has tended to show that in the cerebral hemispheres and, indeed, 

 in the cortex of gray matter lies the seat of consciousness. 

 It is perhaps still an open question as to the existence of a 

 conscious or psychical factor in the activities of other parts of the 

 nervous system, but there is no doubt that the highest develop- 

 ment of psychical activity in man is associated with the cortical mat- 

 ter of the cerebrum. In the young infant the dawn of its mental 

 powers is connected with and dependent on the development of the 

 normal cortical structure, while in extreme age the failure in the 

 mental faculties goes hand in hand with an atrophy of the elements 

 of the cortex. If this cortex were removed all the intelligence, sen- 

 sation, and thought that we recognize as characterizing the highest 

 psychical life of man would be destroyed, and abnormalities in the 

 structure of this cortical material are accepted as the probable 

 causal factor of those perversions in reasoning and in character 

 which are exhibited by the insane or the degenerate. The cortical 

 gray matter, therefore, is the chief organ of the psychical life, the 

 tissue through whose activity the objective changes in the external 

 world, so far as they affect our sense organs, are converted into 

 the subjective changes of consciousness. The nature of this reac- 

 tion constitutes the most difficult problem of physiology and psy- 

 chology, a problem which perhaps is beyond the possibility 

 of a satisfactory scientific explanation. For it is held that 

 the methods of science are applicable only to the investiga- 

 tion of the objective that is, the physical and chemical changes 

 within the nervous matter, while the psychical reaction is of a 

 nature that cannot be approached through the conceptions or 

 methods of physical science. In other words, there is a physicochem- 

 ical mechanism in the brain matter which is capable of giving us a 



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