SLEEP 531 



detached fragment which may be occupied in weaving dreams, has 

 subsided into quiescence. 



It is the variety of our environment and the intensity of rapidly 

 succeeding sensory impulses which keep us awake, by forming new 

 "channels" which intersect with other channel-systems, i. e., arouse 

 "associations" and keep up a continuous activity over the whole area 

 of consciousness. If the Field of Consciousness is limited, either by 

 fatigue or by the limitation of incoming sensory impressions, one 

 group after another of channel-systems or interconnected memory- 

 traces sink into quiescence until only the least fatigued or the most 

 intensely stimulated channels are awake. When the stimulation is 

 nowhere sufficient to rise above the threshold of consciousness, we 

 have sleep, but where the stimulation is intense, and yet excessively 

 circumscribed, we have the condition of Hypnosis. The extraordinary 

 vividness of the impressions which are formed under hypnosis is due 

 to the isolation of these impressions and to the fact that for the moment 

 the brain is, for all effective purposes, limited to and circumscribed by 

 the areas which are directly stimulated. 1 Inhibitive and conflicting 

 impressions are temporarily in abeyance. 



The customary method by which we recollect past events is the 

 Association of a present event with an incident which recalls the past. 

 In other words a stimulus of the present moment happens to traverse 

 a previously formed system of trace-deposits. If, however, only a small 

 portion of the brain be active the chance of a subsequent impulse 

 traversing it must obviously be less than when the area of stimulation 

 is larger. The cutting off of sensory impressions in sleep and the 

 diminution of the extent and variety of "canalization" or trace-for- 

 mation throughout the upper portion of the central nervous system 

 which accompanies sleep is therefore conducive to Amnesia or lack of 

 ability to recollect the intellectual events which occur under these 

 circumstances. This fact is well illustrated by phenomena which fre- 

 quently attend the onset of sleep. A certain sequence of ideas arises in 

 the consciousness we think of it, as we say, dreamily then suddenly 

 this train of ideas vanishes and another takes its place, and we find 

 that we cannot recollect the first. This amnesia is occasionally so 

 surprising in itself that the wonder of it excites us to the extent of 

 awakening. So the cessation of canalization in one trace-system 

 leads, by the blocking off of impulses, to its cessation in an adjacent 

 system, and amnesia spreads over a wider and wider area, until finally 

 sleep supervenes. The fabric of intercommunicating trace-systems 

 which constitutes the waking consciousness shows larger and larger 

 rents of amnesia, the fragments of the fabric are less and less bound 

 together, until at last the entire fabric seems to be blotted out, or one 



1 The impressions received during hypnosis are usually separated from the waking 

 impressions by a gap of amnesia, but during the actual period of hypnosis the extra- 

 ordinary vividness of the impressions received is testified by the almost automatic 

 response of the body to commands or suggestions which are received in this condition. 



