ON MEMORY 193 



ble thereby, even though the cylinder was revolved 

 forever and ever ? 



Leaving analogy and applying the same line of 

 reasoning to our problem, it follows that memory 

 depends on the peculiarity of the nervous system 

 referred to in the first paragraph on page 75, 

 Chapter III, without which it would be inconceiv- 

 able, if not impossible. 



Two other hypotheses to account for memory 

 have been current. The first differs from the one 

 above detailed, in that it supposes the alterations 

 or markings to occur in the tissues surrounding the 

 nervous system. This can hardly be maintained in 

 the absence of evidence to sustain it. 



For it is an obvious fact that the external causes 

 act directly on the nerves. If they act at all on 

 the tissues surrounding them (and this is so far 

 not known), they can only do it indirectly. This 

 can, therefore, not claim to be more than a mere 

 guess. 



The other may be described as follows : From each 

 kind of external causes the impulses are transmitted 

 to special nerves located in special parts of the body, 

 and these nerves are specialized to receive impres- 

 sions of that kind only. By this hypothesis, do these 

 impulses produce no permanent alterations or mark- 

 ings on these nerve-cells. But because these cells 

 are specialized to this class of phenomena only, there- 

 fore whenever a current of energy passes through 

 them then the sensations which distinguish that 



