INTRODUCTION 17 



both the psychologist and the physiologist to make 

 ventures. It is fortunate, nevertheless, that a great many 

 facts can be noted and discussed without any reference to 

 supposed mental states in animals. 



We can deal with all the reactions brought about 

 through the nerve-centers in the simpler animals without 

 assuming psychic accompaniments, and the same method 

 carries us very far with our attempted analysis of nerve 

 physiology in the higher forms. A man cannot regard 

 his own brain in quite the same way in which he regards 

 his liver, but when he is bent on studying the living nervous 

 system in a frog, a cat, or even in another human being 

 his immediate concern is with what it does not with what 

 is felt while the action is in progress. Eventually he is 

 obliged to consider sensation in connection with his other 

 problems, but it is well to defer as long as possible the 

 admission of psychologic elements. 



In accordance with what has been said, an objective 

 treatment of the nervous system will be pursued for the 

 present. The nerves will be looked upon as conductors 

 of energy. The chief source of this energy will be recog- 

 nized in the external forces which are brought to bear 

 upon the organism and which are termed stimuli. The 

 destination of the currents of energy will be found in the 

 contractile and secreting tissues whose activities they 

 modify. Life that is not one's own is manifested through 

 movement, heat production, and secretion; it is very 

 rarely that we are obliged to take other responses into 

 account. Attention must be directed to the fact that 

 nervous tissues separated from others can scarcely give 

 clear evidence of their internal changes. Muscles and 

 glands are required to testify to what is passing in the 

 governing mechanism. (Except for certain electric symp- 

 toms of very slight intensity we should not be able to 

 decide whether a detached portion of a nerve-trunk were 

 living or lifeless.) 



