CH. IV.] SUBSTITUTION OF NERVE-ACTIONS. 293 



in so far as the movements are at least in part dependent 

 on it. 



ii. That the reason why the sentient actions of the instincts, 

 although only incidental, are much more frequently excited as 

 nerve-actions by the vis nervosa of the external impression 

 only, than those of the passions, is this : namely, that the ex- 

 ternal sensation which excites an instinct, being seldom or 

 hardly an object of consciousness to the animal, is in closer 

 relation with the sensational volition of the conceptive force 

 than in the passions ; in which other sensational conceptions, 

 altogether foreign to the primary external sensation, are so 

 widely removed from it, that the sentient actions are quite 

 incidental and excited by them according to psychological laws. 



569. Although the vis nervosa can excite the sentient 

 actions of the passions generally, it cannot imitate the opera- 

 tions of the cerebral forces, in the order in which they are 

 developed psychologically, from the primary external sensation 

 to the outbreak of the passion, unless the latter, like instincts, 

 depend directly, or for the most part, on the sensation. Now 

 since the other results in the animal economy, which peculiarly 

 characterise each passion, are caused by the sentient actions of 

 the passion, by means of the natural connection of all the 

 forces of the animal body, they can be induced by the vis 

 nervosa of the external impressions which excite the passion 

 only under the same conditions. Thus, the sentient actions of 

 joy, namely, the quicker and more vigorous action of the heart, 

 the half-convulsive movement of the diaphragm in laughter, 

 and the volitional movements of dancing, singing, &c., may all 

 be induced by the vis nervosa only, as has been already fully 

 shown. But if the attempt be made to trace the greater 

 number of the joyous emotions to their primary sensations, 

 and to deduce their sentient actions and their other animal 

 movements from their impression alone, as for example, from 

 the nerve-actions caused by wine, or by music, or by a look, 

 or conversation, observation will not afford an instance in which 

 these flow directly from the external impression, except in 

 those cases in which the emotion arises directly from external 

 sensation, like the instinct for pleasure. Such is the case when 

 a chrysalis writhes and turns about if placed in the sun, as if 

 from the pleasurable sensation of warmth ; or when a torpid 



