CHAPTER III. 



ON THE VIS NERVOSA OF INTERNAL IMPRESSIONS 

 (WITHOUT CONCEPTIONS). 



SECTION I. 



482. Every internal impression is transmitted along the 

 nerves, in a direction from the brain downwards^, and is a mo- 

 tor force not subject to physical or mechanical laws (32, 121). 

 If it be caused by conceptions at the cerebral origin of the 

 nerves, the movements it excites are sentient actions (122), 

 but if it be not caused by conceptions, then the movements it 

 excites are nerve-actions of its vis nervosa, and it is of these we 

 propose to discourse. 



483. Non-conceptional impressions, that is to say, internal 

 impressions not caused by conceptions, consequently not origi- 

 nating from a material idea in the brain (123), can take place 

 at any point of a nerve, even at its cerebral origin, but always 

 excepting the terminal fibrils, for it would then be an external 

 impression (32, 121). Consequently, the indirect nerve-actions 

 of external impressions are nerve-actions of non-conceptional 

 internal impressions (422). 



484. Since every internal impression on the nerves is pro- 

 pagated downwards only (141) — if made on a nerve between its 

 origin and termination, it cannot be transmitted as an internal 

 impression upwards to the brain, nor can it excite any animal 

 actions in the parts situate above the point of impression; and 

 if such result, they must be considered as being excited by a 

 concurrent external impression, transmitted upwards to the 

 brain, and consequently are either sentient actions of external 

 sensations, or indirect nerve-actions of the external impression; 

 although, in the latter case, nerve-actions of another internal 

 impression (419, 422). Supposing the trunk of a motor nerve 

 is irritated by a needle, its medulla receives an external im- 

 pression, which is transmitted upwards, and, if it reaches the 

 brain, excites sentient actions by means of an external sensa- 



