522 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



attempt the consideration, partake of the same general character; 

 they assume that the previous repetition or performance has left some 

 species of more or less permanent modification in the nervous system, 

 and they vary only in the nature of this hypothetical modification. 



Broadly speaking, the nature of this modification may be conceived 

 in either of two ways which, for convenience sake, we may designate, 

 respectively, the "static modification" and the "dynamic modifi- 

 cation." The static conception, as developed especially by Munk 

 and Ziehen, regards the "trace" or "image," which has been formed 

 in the nervous system in consequence of some act or repetition, as 

 consisting of some structural modification, some physical alteration, 

 an alteration, in other words, in the distribution of cell-matter in space. 

 The objections which may be and have been urged against this view 

 are manifold. A purely physical alteration, namely the redistribution 

 of preformed cell-material in space, would be something of the nature 

 of a strain produced in response to some stress (= stimulus) which 

 might be conceived of as mechanical, electrical, thermal or yet some 

 other type of energy-change capable of inducing modifications of the 

 physical state of matter. Now the remarkable Persistence of Memories 

 proves that the "trace," whatever it may be, is rather permanent and 

 only very slowly fades away. Indeed such investigations as those of 

 Prince or Sidis would appear to indicate that a large proportion of 

 memory-traces may persist in some measure throughout a lifetime. 

 Of course, reinforcement of the trace by occasional "recollection," 

 either conscious or "subconscious" may have occurred from time to 

 time in the interval between the receipt of an impression and its emer- 

 gence from consciousness under abnormal psychological conditions, 

 such as those imposed by Hypnosis, at a much later period of life. 

 Reinforcement of the trace by recollection cannot, however, be the 

 general rule, for otherwise, as Sidis has pointed out, our entire mental 

 life would be occupied in recollecting. 



The memory trace, or at least some residual fragment of it, is there- 

 fore an extraordinarily persistent modification. The material of which 

 the central nervous system is composed, however, is largely fluid or 

 semifluid, and all our experience teaches as that a fluid cannot retain 

 physical strains for any prolonged period; indeed it is this quality 

 which enables us to recognize a fluid or a jelly and distinguish it from 

 a solid. 



A modification of the theory of Munk is that which was proposed 

 by Lepine and Duval and has been very widely adopted by a certain 

 school of neurologists and psychologists. This theory is based upon 

 the demonstration by Cajal that the nervous system is divided, like 

 other tissues, into distinct cell-units, or Neurons, which he regarded 

 as being in contact with one another through the medium of their cell- 

 processes or Dendrites, but not physically continuous with one another. 

 It was assumed by Lepine that the formation of a new memory-trace 

 in the nervous system was attributable to the formation of a new den- 



