74 CEREBRAL FORCES. [i. 



ii. It may be, also, that many nerves are not adapted natu- 

 rally, or become unadapted to the internal impressions of many 

 conceptions (material ideas), although the change caused by 

 the material ideas really involves their origin ; and that only 

 certain kinds of conceptions (material ideas) can affect them, 

 just as certain external impressions only are received by the 

 nerves (47, ii). An agreeable taste, for example, or the imagi- 

 nation or anticipation of it, cannot excite the sentient actions 

 of vomiting, while an unpleasant taste, or the imagination or 

 anticipation of it, produces that effect. Although both sensations 

 pass along the same nerve to the same origin in the brain, and 

 there excite a material idea, and both ideas or anticipations 

 must develope their material ideas or impressions at the same 

 point in the brain (124), yet, from the one kind the sentient 

 action of vomiting results, but nothing from the other. 



iii. Internal sensations and other conceptions may some- 

 times be so feeble, that they do not make so powerful an im- 

 pression in the brain as is necessary to the production of a 

 sentient action ; and this is also the case with sensations from 

 without (47, iii). A slight irritation of the nose, for example, 

 by snuff, does not produce, as a stronger would, the sentient 

 action of sneezing (80); thus it is, that the phantasies being 

 weak in dreams, we omit many voluntary movements which we 

 should otherwise perform, if the latter were as strong as in the 

 waking state, or as in somnambulism. In these cases there 

 is doubtless an impression in the brain from very feeble con- 

 ceptions (25, 121), only it is not propagated along the nerves 

 to its destined point, but is lost, as it would appear, in the way. 



137. iv. The bifurcations and the ganglia of the nerves may 

 act as impediments to the transmission of internal impressions 

 and to the consequent production of sentient actions, just as 

 they prevent the transmission of external impressions, and the 

 consequent production of material external sensations (48). 

 That this must be the case, is demonstrable from numerous 

 facts. The acquisition of skill in the manual arts depends on 

 a removal of these impediments. It is falsely termed habit, 

 but it is really eocpertness. The frequent repetition of the same 

 impression in the brain, acts each time on the natural hinderance 

 at the divisions of the nerves, just as occurs in the action of 

 two opposing forces, when that which continually repeats its 



