I 



. I.] NERVE-ACTIONS IN GENERAL. 209 



a separated muscle is irritated by a physical irritant applied to 

 the medulla of the trunk, or when an external impression is 

 reflected in the muscle itself and becomes an internal im- 

 pression, ia either case movement of the muscle may result, 

 without it necessarily following that the motor force is situate 

 in the muscular fibres, independently of the nerves. Unless 

 it can be proved that the irritant which moves a muscle, whose 

 nerves are divided, cannot have excited a non-conceptional im- 

 pression in the medulla of the nerve, whether by causing a 

 mere physical irritation of the latter, constituting an internal 

 impression, or by the reflexion of an external impression in 

 the muscle itself, and that the movement of the muscle is not 

 produced by such impression, it cannot be allowed that the 

 peculiar animal force of the muscular fibre is demonstrated by 

 the experiment (380). 



382. But perhaps, it may be urged, a muscle may be so 

 irritated, as to be excited to movement without the irritant 

 causing at the same time an impression on its nerves, for it 

 is not every excitant which causes an impression (32) ; and 

 possibly the muscular fibres are excited to movement by 

 irritants which do not animally affect the nerves. 



This proposition would be of importance, if it had been pre- 

 viously shown that muscular fibres are capable of movement, 

 independently of their nerves ; but this condition is wanting. 

 Besides, facts prove that the impressions which move muscles 

 affect also the nerves, because they can be felt. We will, how- 

 ever, notice the leading points which Haller advances in 

 defence of his doctrine. 



383. Haller observes that muscle is excited to movement 

 when touched, but nerve is not. Consequently, this irritability, 

 or the property to be moved animally, from a certain contact, 

 is proper to muscular fibres rather than to nerves. May not, 

 however, they possess this property simply through their nerves ? 

 If the muscular fibres constitute a mechanical machine, excited 

 to movement by suitable impressions on its nerves, it is the 

 machine that possesses this capability of movement rather 

 than the nerves themselves, for an impression never visibly 

 excites movement in the nerves, but in the mechanical machines 

 with which they are incorporated (153). The same applies to 

 all movements of muscle excited by conceptions, or by the will. 



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