24 BIOLOGY AND SOCIAL PROBLEMS 



whole life, from the memorandum on a scrap 

 of paper to the inscription on the living rock, 

 and thus aids enormously one of our mental 

 processes at its weakest point. 



How is memory related to the nervous sys- 

 tem ? By appropriate methods of experimen- 

 tation we can determine with great accuracy 

 the tracts of the nervous system over which a 

 given reflex runs. Is such a localization pos- 

 sible for memory, or is this function rather the 

 general property of the nervous system as a 

 whole? Strange as it may seem, memory is 

 almost if not quite the exclusive function of 

 one part of our nervous organs, namely, the 

 cerebral cortex. This gray layer covers the ex- 

 terior of the cerebral hemispheres and thus 

 lies on the surface of the brain separated from 

 the outer world by only the skull and the 

 superimposed scalp. In man it varies in thick- 

 ness from one and a half to five millimeters 

 and covers a convoluted field, which, were it 

 flattened out, would measure on the average 

 2352 square centimeters, equal to an area a 

 little over a foot and a half square. This re- 

 markable layer is the organ in which all our 

 sensations arise and where the processes of 

 memory go on. It is, therefore, the location 



