I 



ti. I.] NERVE-ACTIONS IN GENERAL. 211 



the nerves. (Compare 362, iv, and 367, ii, for a further cor- 

 rection.) 



387. The movements dependent on nerves (Haller states) 

 cease with life, those on the vis insita continue after death; 

 destruction of the brain, or ligature of the nerves, prevents the 

 former, the latter continue without brain. Parts that have no 

 sensation are moved, others that have are not moved; the 

 will excites or arrests the nerve-motions, it has no power over 

 the actions of the vis insita. 



All this only demonstrates the difference between the cere- 

 bral [animal -sentient] forces and the nerve -forces, between 

 sentient actions and nerve-actions. It does not prove, how- 

 ever, that the nerve-actions are not produced through the 

 nerves, but that they are not produced through the brain or 

 the mind. 



388. It does not appear then, that this doctrine of Haller 

 can be supported by valid arguments. There are other ob- 

 jections to it. No irritant applied to parts un supplied with 

 nerves, can excite movements. Then irritability is peculiar 

 to muscular fibre, but all muscular movements are motions of 

 mechanical machines intimately connected with the nerves, and 

 the latter cannot be entirely separated from them without at 

 the same time destroying their structure. Every impression 

 which excites the muscle irritates also the nerves. An internal 

 impression on the medulla of the nerves, excites the same move- 

 ments as when the muscular fibres are irritated. Opium, 

 which if applied to a nerve deprives it at the point where ap- 

 plied of its vis nervosa J also suddenly renders a muscle unirri- 

 table at the point of application (Whytt's Works). Every nerve 

 retains the animal motor force, even if cut, or tied, or otherwise 

 so treated that an external impression on it can no longer be 

 felt (381, i); and, in fact, the same muscular action is excited 

 by an irritant, whether it be felt or not (204, 357). Now since, 

 therefore, all muscular movements which are attributed without 

 adequate grounds to the irritability of muscles can also take 

 place in virtue of impressions on their nerves, and in undoubted 

 instances actually do so take place, and as there is no reason 

 why they should not occur in every case, so soon as the muscular 

 fibre is irritated, it is probable that no truth in all physiology 

 is so physically certain as this ; that all animal movements of 



