LOCALISATION OF FUNCTION. 275 



interpreted to mean either that before maturity there 

 exist pathways which later cease to be permeable, or, the 

 lesion occurring before maturity, that under the new and 

 abnormal condition fresh connections are established by 

 compensatory growth, the capacity for which growth is 

 later lost. In man, of course, the paralysis of a limb 

 caused by injury to the adult cortex is permanent, and 

 there is no suggestion that the other hemisphere acquires 

 a subsequent control of both halves of the cord, but a 

 similar lesion may be far less damaging when it occurs 

 in a child. 



This leads to the question of the relative importance 

 of the two cerebral hemispheres in man. It is probable, 

 from all that can be ascertained, that in a thoroughly 

 ambidextrous individual the two hemispheres more 

 nearly correspond in their functions than they do in the 

 one-handed individuals, as represented by the majority 

 of the community. It is certain, however, that while in 

 the strongly right-handed persons it is the left hemi- 

 sphere which is mainly concerned, the reverse is the 

 case in those left-handed. For example, in the average 

 right-handed person the entire series of disturbances 

 which are grouped under the term aphasia, occur as the 

 result of injuries to the left hemisphere. Seeking to 

 explain this, we recognise that the sense organs con- 

 nected with injured hemispheres are most naturally asso- 

 ciated with the motor centres of the same side ; but even 

 if this is granted, the manner in which this peculiarity 

 was acquired, and the duties of the other hemisphere, 

 remain still unexplained. Though in children injury to 

 one hemisphere may be compensated by the develop- 

 ment of the other, in the adult such is not the case. 

 Normally, too, the hemispheres attain nearly the same 

 weight, and there is no evidence that the left hemi- 

 sphere is persistently the heavier in a right-handed 



