THE CEREBRUM 273 



be that every afferent fiber in the system exerts an influence 

 thus indirectly upon the organ of the will, and the impressions 

 conveyed by them are reflected in one's character and life. 

 But it cannot be said that all voluntary activity is thus of a 

 reflected nature; there is some cause other than the reception of 

 afferent impressions which sets the will in operation. 



Connection Between the Brain and Intelligence. It is 

 claimed that a single hemisphere is capable of performing all the 

 ordinary intellectual acts as well as both; and atrophy, or de- 

 struction otherwise, of one hemisphere has frequently been no- 

 ticed to entail no mental defect. But whether the mind under 

 such conditions would be equal to the highest intellectual attain- 

 ments is doubtful. It would seem that in health the brain unites 

 the impressions received by the two sides (as, e. g., through the 

 optic nerves), and the resulting idea is a single one; that is to say 

 a person does not have two opposing ideas about the same thing 

 the same time; the two hemispheres seem to agree. 



In a general way, it may be stated that the degree of intelli- 

 gence corresponds to the weight of the brain, though to this 

 rule there are many exceptions. It may be more properly said 

 that the development of the intellectual faculties is greater as 

 the area of gray matter is increased by the convolutions of the 

 cortex. Idiots' brains are usually, though not by any means 

 invariably, much below the average weight. 



A difference in intellectual vigor may be present in persons 

 whose brain shave the same weight and even the same amount of 

 gray matter. A difference in the quality of the gray substance 

 may in such cases account for the varying results. It is a matter 

 of common observation that mental exercise increases mental 

 vigor and capacity, just as muscular exercise develops muscular 

 strength. It is difficult to reach a conclusion as to whether there 

 is an increase in the amount of gray substance or whether that 

 already present is endowed with additional power. 

 18 



