CH. II.] CEREBRAL IMPRESSIONS. 71 



are appropriate to the sentient action, as to be transmitted (121); 

 in this case, the impression must be made on those fibrilli of the 

 nerve which propagate it from the brain outwards (126, 127). 

 ii. That the further transmission take place, as stated in iii 

 and iv of last paragraph. 



131. When the material idea of an external sensation makes 

 an impression on the origin of another nerve than its own, it 

 becomes the material idea (121) of another (118), and indeed 

 of a sensational conception ; or of instincts and passions by 

 means of the sensational stimuli of thie conception (88, 90, 91) ; 

 and, consequently, of analogous purer conceptions, which 

 although induced by means of external sensations, are also 

 spontaneously (27) developed, as stated in § 130. 



132. The medulla of the nerves is naturally adapted to the 

 external impressions of the external sensations (31) ; but since 

 it is no other than cerebral medulla, the latter is also naturally 

 adapted to external impressions. When, consequently, certain 

 fibrilli of the cerebral medulla are touched or stimulated, they 

 receive an external impression (just as the terminating fibrilli 

 of the nerves), which is propagated along the fibrilli to their 

 cerebral origin (45, ii), and there excites a material external 

 sensation. This latter causes an impression on the brain, 

 which either produces sentient actions directly by means of a 

 nerve at that point, or in the way stated in last paragraph. 

 Consequently when the cerebral medulla of living animals en- 

 dowed with conceptions is irritated, an external material sen- 

 sation is produced (as for example that belonging to pain), 

 which produces sentient actions through the nerves (e. g., 

 convulsive movements from pain), in the same way as other 

 external sensations (129, 130, ' Haller's Physiol.' §368). 



133. In proportion as the cerebral impressions, and the forces 



I which excite them, namely, the external sensations (129), and 

 the spontaneous mental conceptions (130) are powerful, in the 

 same proportion the sentient actions which they excite through 

 the nerves are vigorous (121, 26). 

 134. A sentient action produced directly through the nerves 

 by an external sensation may be prevented : 

 i. By everything which prevents the external sensation 

 (46, 129, i.) 

 ii. By this, that the material external sensation in the 

 I 



