258 SCIENCE AND IMMORTALITY 



Physiologically considered, the molecular vibra- 

 tions which are the concomitants of sensation and 

 thought are situated in the nerve-cells spread over 

 the surface of the brain, forming a layer known as 

 the " grey layer." When these cells are destroyed, 

 thought and sensation and voluntary movement 

 are abolished. Certain areas of grey matter are 

 concerned specially with movements, others with 

 hearing, others with thinking. Thus, if a certain 

 group of cells in the posterior part of the third left 

 frontal convolution is destroyed, power of speech 

 is lost. Thinking powers seem to be located 

 chiefly if not entirely in the frontal lobes (those 

 behind the brow), but the special faculties, mathe- 

 matical, philosophical, etc., have not been located — 

 indeed it is doubtful if there be such a thing as 

 separate faculties, and the " bumps " of the phren- 

 ologists have no sort of relation to the faculties 

 they are said to represent. 



In a general way it may be said that good 

 frontal development is usually associated with 

 mental power ; but between the total weight of 

 the brain and mental ability there is no constant 

 connection. Idiots have sometimes very large 

 brains and clever men sometimes small ones, and 

 the following tables will show how little connection 

 there is between weight or size and ability. 



