292 ANIMAL FORCES. [ii. 



those machines into motion, which must act in flight and 

 defence from the foreseen danger (315, 319), whence all the 

 other phenomena result (316, 320). All these sentient actions 

 may be excited as nerve-actions, in decapitated animals, insects, 

 or frogs, or in a decapitated man, or in an acephalous foetus. 



567. Not even the same kind of passions arise always from 

 external sensations in the same way, but sometimes directly 

 from them, sometimes with the intervention of many psycho- 

 logical conceptions. When a dog is frightened by a sudden 

 blow, so that it excites its muscles for the purpose of running 

 away, it connects with the external sensation of the blow, the 

 foreseeing excited by frequent experience, that many more 

 blows will follow, and thus the emotion of fear arises, without 

 the intervention of other conceptions. This sentient action of 

 fear can be developed by the vis nervosa only of the same ex- 

 ternal impression, and would be manifested if the animal were 

 decapitated (555). If, on the other hand, fear is excited in a 

 man by a sudden blow, it may arise from a sensational concep- 

 tion, which has little in common with the sensation. He judges, 

 for example, that the blow must have been inflicted by a man : 

 he looks about, and sees no one. This excites surprise and 

 thought, and he now concludes from probabilities : firstly, he 

 thinks it may have been from a concealed robber, and thus fear 

 incites him to those sentient actions which can protect him : 

 then he conceives it was a ghost, and fear incites him to run 

 away : lastly, he attributes the blow to some missile, and fear 

 incites him to hide himself, &c. The impression of the blow 

 could not possibly excite all these various kinds of sentient 

 actions, since so many volitional conceptions influence them ; 

 the external sensation only excites the will into action. 



568. We conclude, therefore, from the preceding statements : 

 i. That the sentient actions of the passions generally may 

 be excited by means of the vis nervosa only (563) ; but that 

 the same external impressions, which by means of their corre- 

 sponding external sensation induce the passions, however 

 remotely (66, 90), can only excite by the vis nervosa the move- 

 ments constituting the sentient actions of the latter, in so far as 

 these actions, although always incidental to the external sensa- 

 tion excited, are not produced by intermediate conceptions, in- 

 duced by other sensations differing altogether from it, and only 



