UNCONSCIOUS MEMORY 101 



We find a beginning in the non-living world. Some 

 record of each stimulation survives in the structure of 

 the object stimulated. The steel of a bridge slowly 

 becomes crystalline as trains continue to pass over 

 it. In this case the memory, so to say, is permanent. 

 A steel spring set to vibrate after a time responds 

 less to the same stimulus ; it has become " fatigued," 

 but if it be allowed to rest, it recovers tone. In this 

 case the memory is short. Often in the last few 

 miles of a long motor drive, I have found the engine 

 not " pulling " so well ; next morning, although 

 nothing has been done to it, it has forgotten the 

 fatigue and runs as well as ever. Gelatine melts or 

 congeals at a definite temperature according to its 

 composition, but a previous melting or congelation 

 alters the point of temperature at which subsequent 

 melting or congelation occurs. A beam of polar- 

 ized light when passed through gelatine is rotated, 

 but when the operation is repeated, there is a greater 

 rotation for the same stimulus. I do not know how 

 long these memories last in gelatine. From the phy- 

 sical point of view, protoplasm is not very far removed 

 from gelatine, although it is certainly much more 

 complex chemically, and of more elaborate physical 

 structure, even in its simplest forms. Very roughly 

 it may be said to differ from gelatine in the same sort 

 of fashion that a complex machine like a motor car 

 differs from a simple structure like a steel spring. 

 It is therefore not surprising to find that the effect 

 of a past stimulus is registered in protoplasm, more 

 or less evanescently, so that repetition of the same 

 stimulus produces a different response. The experi- 

 ments and observations of many investigators who 



