ciu XVI.] THE EVOLUTION OF MI^D, 155 



a single ganglion, where an appreciable time must elapse 

 before they are carried off each along its own set of transit- 

 lines. For exan)ple, when ynu tickle or pindi the arm of a 

 person asleep, the arm is at first withdrawn by simple reflex 

 action : the ordinary channel, through the afferent nerve tc 

 the spinal centre and back again through the efferent nerve tc 

 the limb, suffices to carry off all the molecular disturbance, 

 — and there is no consciousness of the irritation or of the 

 resulting contraction. But if the pinching be frequently 

 repeated, so that the disturbance is generated faster than it 

 can be thus drafted off, the surplus is sent up through a 

 centripetal fibre from the spinal ganglion to the brain ; and 

 some dreaming ensues, or perhaps a fretful sound is emitted. 

 If the impression be kept up long enough, there is full con- 

 sciousness of it, and the person awakes. Now the rise of 

 consciousness implied in the dreaming and waking is due to 

 the persistence in the cerebrum of a molecular disturbance 

 which is not at once drafted off through the proper centrifugal 

 fibres. 



Obviously, therefore, when the number of impressions sent 

 in to the brain from moment to moment exceeds the number 

 of thoroughly permeable channels which have been formed 

 there, so that there is a brief period of tension during which 

 occur the nutritive changes implied in the transmission of the 

 disturbance through the appropriate channels, then there 

 arise the phenomena of conscious intelligence. For mark 

 what must happen. In the Jlrst place, the persistence of 

 the impressions enables them to be consciously felt, either 

 pleasurably or painfully ; so that there is the germ of Emo- 

 tion. Secondly, the disturbance tends to propagate itself 

 along various permeable transit-lines, so that there is a 

 revived association of ideas, or what we call Memoiy. 

 Thirdly, there is an integration of the present impressions 

 with such past ones as they resemble, and a differentiation of 

 them from such past ones as they do not resemble ; and this 



