THE BRAIN 



733 



manner we have no knowledge. The sensations of the present moment 

 may arouse one or other of these memories to which it is attuned. 

 Our actions are controlled from moment to moment by the sensations 

 which stream in at the present time, and the memories of past sensa- 

 tions which are aroused by these. 



Our knowledge, opinions, and beliefs are, then, the result of the 

 supply of sensations furnished by impulses acting on the brain struc- 

 ture. Without such sensations, no mind or consciousness would be 

 manifest. The extero-ceptive mechanism plays an all-important part. 

 This is well seen in the case of Helen Keller, who, deaf and dumb, 

 and uneducated, when her eyes were* closed, fell asleep. 



Memory forms the basis of our experience and knowledge, and our 

 so-called voluntary actions, initiated by the cerebrum, result as in- 

 evitably as a spinal reflex action from the synthesis of present and 



To touch, 

 14 sec. 



To hearing, 

 16 sec. 



FIG. 448. REACTION TIMES TO TOUCH, HKARING, STOUT. (Waller.) 



memorized sensations, some of which inhibit, and others facilitate, 

 motor response. Education thus becomes of supreme power in 

 moulding the actions of a man's life. 



As the pattern of the brain is ceaselessly altered by instreaming 

 sensations and metabolic processes, the personality of a man alters 

 from moment to moment. The babe develops into the man of genius, 

 and he, if he lives long enough, becomes a dotard in his old age. By 

 the time he is in his second childhood the personality of his prime 

 manhood has left him, for this depends on characteristic responses to 

 sensations, and these can no longer be aroused in a brain the structure 

 of which has deteriorated with age, and from which the store of 

 memories has largely vanished. We must remember that the work 

 of a genius is the accumulated result of successive and innumerable 

 moments of interaction of sensations, present and memorized. His 

 output results from the inborn qualities of the sense organs and brain 

 structure on the one hand, and education on the other the storage 

 of his experience and that of humanity handed on by oral or written 



