296 ANIMAL FORCES. [ii. 



(342, 445, 507). But since the mind produces all these kinds 

 of motives [Bewegungsgriinde] and desires of the will, according 

 to purely psychological laws, and independently of external 

 impressions (333, 341), the movements resulting cannot be 

 induced like the sentient actions of sensational conceptions, 

 feelings, and desires, by the vis nervosa ; and, although those 

 movements which are excited by the will, in intellectual beings, 

 may and do occur in decapitated animals, or in purely sen- 

 sational animals, still they are induced by impressions, and not 

 psychologically. 



577. The incidental influence which the will exercises, by 

 means of its acts on the animal economy (compare 336, 337, 343), 

 can be exercised also by the vis nervosa, in so far as that in- 

 fluence consists in sentient actions directly dependent on the 

 internal impressions of sensational conceptions, incitements, 

 and desires. 



578. The intellectual conceptions (330), the motives con- 

 tained in them (333), and all desires and aversions of the will 

 (339), in addition to their remote connection with sensation 

 (65), possess a special connection in virtue of the sensational 

 conceptions, incitements, and desires, intermingled with them. 

 Hence all their sentient actions have a sensational character, and 

 to this extent can sometimes be induced by the vis nervosa of 

 external impressions, although always very imperfectly. When 

 the external sensation of a tune excites our instinct to dance, 

 the desire of the will to dance a rhythmical dance is combined 

 with the instinct, and by dancing we satisfy that desire. In so 

 far as this free-will act is a sentient action of the instinct, it can 

 be excited purely as a nerve-action of other impressions : those 

 affected with chorea St. Viti, for example, dance involuntarily 

 and convulsively, even when sleeping, but certainly not ryth- 

 mically, since this is an action of the will. 



579. The following conclusions may be drawn, as to the 

 substitution of nerve-actions for sentient actions. All move- 

 ments which can be sentient actions may be excited, either 

 as nerve-actions only by the vis nervosa alone, or as the latter 

 at the same time that they are sentient actions (503); and so 

 far as it is possible to illustrate the question by observations and 

 experiments, the latter establish this principle without exception. 

 If, however, the sentient actions be considered in reference to 



