PHYSIOLOGY 



409 



that is of great moment in elucidating the relations of 

 brain and mind— has been known for only a little more 

 than thirty-five years. For it was in 1871 that Fritsch 

 mid Ilitzig. liy stimulating specific small areas of the sur- 

 face of the cerebrum and obtaining in response specific 

 muscular movements, first demonstrated a specific cere- 

 bral localization of functions. Since then the task of 

 mapping out the outer layer, or cortex, of the cerebrum 

 of a few mammals and man into centers, joined by nerve 

 fibers with specific organs of the body and employed for 

 the control of separate groups of muscles and for the 

 work of the special senses, has proceeded to a consider- 

 able degree. Thus, we are now able to point to a 

 certain portion of one of the convolutions of the cerebrum 

 and say that its nerve cells, or neurones, mediate the voli- 

 tional act of contracting one's biceps muscle; we can say 

 that the neurones in oilier localities mediate the separate 

 acts involved in locomotion; in others, the changes of 

 facial expression; and in still others, the enunciation of 

 thoughts in the form of spoken words. We know with 

 considerable exactness the positions of the separate 

 centers for sight and hearing; less exactly those of the 

 other special senses. Besides the sensory and motor 

 centers, evidence points strongly toward the existence 

 also of cortical regions which are elaborately joined to 

 one another and to the sensory and motor regions by 

 means of innumerable nerve fibers, and the function of 

 which is to correlate, harmonize or associate the work of 

 the sensory and motor centers. Such association centers 

 thus help to mediate the more complex psychical phe- 

 nomena, such as memory and the association of ideas. 

 We can even formulate helpful hypotheses of the neural 

 accompaniments of various psychoses. According to 

 James's theory of the emotions, for example, the per- 

 ception of the automobile about to run us down leads to 

 the feeling of fear only through the mediation of various 

 organic i)rocesses, such as a quickening of the heart beat, 

 pallor and trembling. The accompanying series of 



