214 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



time reproduce its visual image in our memory, or, 

 even more than that, it will reproduce the recollection 

 of scenes or persons who were present when the same 

 odour made its first strong impression on us. By 

 associative memory we mean, therefore, that mechan- 

 ism by means of which a stimulus produces not only 

 the effects which correspond to its nature and the 

 specific structure of the stimulated organ, but which 

 produces, in addition, such effects of other causes as 

 at some former time may have attacked the organism 

 almost or quite simultaneously with the given stimu- 

 lus (2). The chief problem of the physiology of the 

 brain is, then, evidently this : What is the physical 

 character of the mechanism of associative memory ? 

 As we said in the first chapter, the answer to this 

 question will probably be found in the field of physi- 

 cal chemistry. 



I think it can be shown that what the metaphys- 

 ician calls consciousness are phenomena determined 

 by the mechanism of associative memory. Mach has 

 pointed out that the consciousness of self or the ego 

 is simply a phrase for the fact that certain constitu- 

 ents of memory are constantly or more frequently 

 produced than others (i, 1 1). The complex of 

 these elements of memory is the " ego " or the "soul," 

 or the personality of the metaphysicians. To a cer- 

 tain extent we are able to enumerate these con- 

 stituents. They are the visual image of the body so 

 far as it lies in the field of vision, certain sensations 

 of touch which are repeated very frequently, the 



