4 



H. II.] NERVE-ACTIONS, EXTERNAL IMPRESSIONS. 237 



hicli it would excite if it were felt and caused a painful or 

 pleasing sensation; but we know no more in what it differs 

 from an impression which produces the contrary effect, than in 

 what sensations themselves differ (190). Nevertheless, it is very 

 probable, that the external impression which would have excited 

 pleasing sensations, operates upon the nerves connaturally or in 

 a way that is in accordance with their normal and appointed 

 functions ; while on the contrary, those which would have caused 

 a painful sensation, act upon the nerves contra-naturally 

 [widernatiirlich] ; consequently, the resulting nerve-actions 

 themselves are either connatural or contra-natural (191, 195). 

 Experiment supports this view. If a decapitated animal be 

 irritated, so that in its ordinary state the irritation would have 

 caused pain, it fights with its natural weapons, as if the pain 

 were really felt; a headless wasp stings, a headless earwig 

 attacks with its nippers, &c. All these movements are violent, 

 convulsive, and contra-natural, just as they are in the ordinary 

 state of the animal. An acrid irritant causes a convulsive con- 

 traction in the excised intestine of an animal, just as usually 

 occurs in the painful colic excited by ths same acrid poison. 

 Gentle stimuli, on the contrary, excite in headless animals 

 gentle movements only; when a decapitated cricket receives 

 the external impressions which ordinarily excite the insect to 

 the act of sexual congress, a disordered and half- convulsive 

 manifestation of the sexual instinct is excited, which borders 

 closely on a contra-natural state, because its sensational stimulus 

 is a titillation of the sexual organs (274). It chirps incessantly 

 with its wings, and allures to se:8;ual congress with unusual 

 energy and activity. 



441. Consequently, just as external impressions follow upon 

 each other, so also the same movements result as nerve-actions, 

 which take place as sentient actions, when the external im- 

 pression excites pleasing or unpleasing external sensations, pain 

 or tickling ; and these nerve-actions are in like manner, either 

 in accordance with the natural destination of the mechanical 

 machines, or opposed thereto. 



442. It is not necessary that an external impression shall 

 always develop indirect nerve-actions in the mechanical ma- 

 chines supplied with fibrils from the nerve which received the 

 impression, or from others in connection with the latter, for 



