1901.] on Memory. 601 



tesimal distortions that are produced by every wave of motion that is 

 incident upon the nervous system, which is so particularly and mar- 

 vellously sensitive to disturbance by small increments of motion. 

 We are justified in supposing that it is by the operation of what I 

 have termed dynamic memory, by which a distortion facilitates sub- 

 sequent distortion in the same sense, that the nervous system has 

 acquired its marvellous sensitiveness to distortion by infinitesimal 

 forces. And it is not a little significant that our conscious memories 

 weaken and fade in much the same ratio to the lapse of time as does 

 the structural memory of the stick. They remain bright and vivid 

 for a short time, then they fade with increasing speed for a time, and 

 then with slackening speed for an indefinite time thereafter. 



The living organism is not only acted on ; it reacts. It is not 

 merely passive ; it is active ; and the mode of its action is deter- 

 mined by its structure. According as the structure is modified, so 

 is the function modified. When a structured memory is formed in a 

 tissue having an active function, all future function, all future action, 

 is modified by the existence of the memory. This modification of 

 function that is conditioned by the formation of a structural memory 

 I call Active memory. So long as the structural memory lasts, so 

 long is each exercise of function modified, and the degree of modifi- 

 cation is in proportion to the degree of set that remains in the tissue. 

 As the structural memory disappears with the lapse of time, so the 

 mode of the function loses its new peculiarity and returns to the 

 former mode. 



Certain regions of the nervous system there are whose activity is 

 accompanied by consciousness. When a new mode of activity occurs 

 in these regions, a new mode of consciousness accompanies the acti- 

 vity. When the activity of that particular nervous process subsides, 

 the accompanying state of consciousness dies away and ceases. But 

 in the tissue is still left a structural memory, such that when that 

 portion of tissue again becomes active, it becomes active in the same 

 way. The process is punctually repeated, and the repetition of the 

 activity, which I call active memory, is accompanied by a repetition 

 of the mode of consciousness, whicli is conscious memory. 



Thus there are four different conditions to which the term memory 

 is applied. There is Structural Memory, which is an alteration in 

 the position of the particles of the tissue. There is Dynamical 

 Memory, which is an alteration among the stresses of the shifted 

 particles. There is Active Memory, which is the altered process tbat 

 takes place in the altered tissue ; and there is Conscious Memory, 

 which is the conscious accompaniment of active memories in certain 

 regions of the nervous system. The three latter forms depend, it 

 will be seen, upon the structural memory, to the consideration of 

 which we may now return. 



It is evident that the entire structure, not only of the nervous 

 system, but of the whole organism, may be regarded as a group of 

 statical memories ; nay more, it is obvious that the same is true of 



