I 



II.] EXTERNAL DIRECT NERVE-ACTIONS. 241 



actions in a muscle (424); nor is it to be inferred, that because 

 certain irritants fail to excite movement in a muscle, it is de- 

 fective in the vis nervosa of an external impression; or because 

 it is excited to movement by some, it must necessarily be so 

 excited by all. Every muscle, like the nerves, has its own 

 special external impressions, which directly irritate it rather 

 than others, and that whether they be felt or not. And the 

 same irritant of the nerves in a muscle may cause an external 

 impression, be transmitted upwards, be felt, or be reflected 

 downwards, and consequently produce sentient actions, or in- 

 direct nerve- actions, and all without having produced a direct 

 nerve-action in the muscle itself (424, iii). 



452. Those external impressions on the muscular fibre which 

 can excite an agreeable external sensation, excite the muscles 

 to movements in accordance with their healthy functions, as 

 the sensations themselves would ; on the other hand, those 

 which would be painful to the animal under ordinary circum- 

 stances, excite the irritated muscle to spasmodic and convulsive 

 actions, and convulse the limbs (204, 440) . Thus acrid, irritant 

 poisons, excite violent writhings in an excised portion of intes- 

 tine, and render an excised muscle hard, and permanently 

 contracted; the excised heart beats irregularly, if strongly 

 irritated, &c. 



4<53. The direct nerve -actions of an external impression on 

 the muscles are the same as the direct sentient actions of its 

 external sensation, and can cause the same series of movements 

 which these latter excite by their pleasure and pain, and the 

 resulting sensational conceptions as incidental sentient actions ; 

 so that external impressions may thus excite a whole chain of 

 apparently volitional acts, without one of them being felt, or any 

 conception whatever excited (437-8). Hence an animal may, 

 by external impressions only, perform all the organic and appa- 

 rently volitional movements necessary to its existence, without 

 having either brain or mind, if its body be so constituted (as is 

 quite possible) that all external impressions on its nerves can 

 produce their direct and indirect nerve-actions, without having 

 to excite material ideas in the brain, or conceptions in the 

 mind, connected therewith. 



454. Although muscular movements be, for the most part, 

 excited volitionallv, either by external sensations or volitional 



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