124 HUMAN PHYSIOLOGY 



own side. The nerve fibres of each half of the brain 

 cross in the upper part of the spinal cord to the op- 

 posite side of the body, and so give us right-handed- 

 ness associated with the left lobe of the brain, as 

 the right side of the brain in turn controls the left 

 side of the body. The left side of the brain is thus 

 figured forth as the superior half or lobe, seeing 

 that its functions are more complex and involve the 

 discharge of more important duties (the conduct of 

 the right hand, for example) than those performed 

 by its neighbour, the right half. To what this 

 superiority and selection of the left half of the 

 brain as the controlling lobe is due, is difficult to 

 determine. Whether this superiority arose from the 

 body acting on the brain, or whether right-handed- 

 ness was developed through the left half of the brain 

 acquiring a dominant power over the right half, it is 

 impossible to say. One important fact, however, 

 teaches us the superiority of the left half of the brain 

 in an unexampled manner. This fact is found in the 

 demonstration that the speech centre of the left side 

 of the brain is that by which the ordinary right- 

 handed mortal exercises this special human gift. A 

 similar speech centre exists on the right side, for the 

 centres of the brain are in duplicate ; but the right 

 centre eems to remain in abeyance, and it is prob- 

 ably only in the case of left-handed persons, whom 

 the right lobe dominates, that speech is controlled 

 from the brain's right side. In cases of the disease 

 known as aphasia, in which the power of speech is 

 lost, while that of the other faculties may remain 

 practically unimpaired, the left speech centre is 

 found to be affected. In cases where this centre 

 has been destroyed and where a certain amount of 

 recovery of speech has taken place, it is believed 



