STRUCTURE AND FUNCTIONS OF THE CEREBRUM 159 



mental processes become simpler and simpler does it follow that 

 consciousness becomes dimmer and dimmer? We ordinarily as- 

 sume this to be true, but without any positive evidence upon 

 which to base the assumption. 



Emotions. Another set of phenomena accompanying cerebral 

 activity, but known chiefly by subjective experience, are the 

 emotions. . We know that certain sensory stimuli give us pleasure, 

 others arouse disgust. Love and hate, sorrow and joy, are mental 

 states which are associated with certain sense impressions im- 

 mediate or remembered. Emotion, like consciousness, does not 

 lend itself to objective study, and therefore does not come within 

 the realm of physiology beyond simple recognition of the exist- 

 ence of the phenomenon. It is true that emotional states are 

 usually accompanied by reactions of other parts of the body, the 

 blush which accompanies embarrassment being an example, but 

 this allows us only to judge whether an emotion is present, and 

 tells us nothing about its actual nature. 



Cerebral Functions Compared in Man and Animals. In the 

 higher animals as well as in man associative memory is the rep- 

 resentative cerebral activity. So far as we can judge it represents 

 in animals the climax of intellectual achievement. No animal 

 has ever been seen to perform any act, not purely reflex, as are all 

 " instinctive" actions, which associative memory cannot account 

 for. The activities of man are for that matter based upon as- 

 sociative memory almost as fully as are those of animals. The 

 important intellectual difference between man and animals is 

 the possession by man of the faculty of reason, which is denied 

 to animals. The power to reason is itself, however, based upon 

 associative memory. It may be roughly explained as the as- 

 sociation of concepts whose relationship is not obvious. An 

 animal, according to this idea, cannot reason because he cannot 

 form associations except of concepts that manifestly belong to- 

 gether. The man reasons by perceiving relationships in appar- 

 ently unrelated facts or ideas. We may illustrate the difference 

 between man and the higher animals by comparing the actions 

 of a man and a monkey in opening a specially fastened door. 

 Suppose the door is held by a catch which is released by pull- 

 ing a pin upward. Both man and monkey will learn to raise the 

 pin and so release the catch; one can open the door as readily 



