CH. I.] NERVE-ACTIONS IN GENERAL. 



exactly similar to those produced in the natural condition by 

 the volitional conceptions : thus, the diaphragm renews its 

 motions as in respiration, if the trunk of its nerve be irritated : 

 thus, the body of a dog, or of an ox, (nay, even of a man, as 

 is seen in executions by decapitation,) will be thrown into the 

 most violent volitional movements, when the spinal cord is cut 

 through : if in such an one the cord be irritated inferiorly, 

 the movements involve the feet only; if superiorly, panting 

 respiration, palpitation, deglutition, and vomiting result. When 

 an irritation of the spinal cord produces spasmodic convulsions 

 of the whole body, but a particular nerve has been previously 

 divided, the limb to which that nerve is distributed is 

 unaffected by spasmodic action, because the irritation cannot 

 be transmitted to it : thus also, a decapitated frog rises up and 

 springs forward, and if thrown into water begins to swim, so 

 soon as its spinal cord is irritated by a needle in the cer- 

 vical region, just as if it knew what it had to do. Bilguer 

 relates a somewhat similar case, in which if a certain part of 

 the neck where suppuration had taken place, was irritated, 

 the patient was obliged to stand upright in spite of himself, &c. 

 A great variety of well-authenticated facts of this kind may 

 be found in Haller^s * Physiology.' 



360. An internal impression on the nerves can produce ike 

 same animal movements in the body, as the co7iceptions produce 

 by means of material ideas, although not caused by conceptions, 

 nor even taking place in the brain. — These movements are 

 animal, for they do not result from physical and mechanical 

 forces only (§ 121. Haller's 'Physiology,' § 412). They do 

 not necessarily occur in connection with conceptions, be- 

 cause the internal impression which excites them need not 

 be a material idea, and it is in no degree necessary that 

 conceptions cause it. These are not, therefore, sentient 

 actions (123), although the two kinds of actions may occur 

 at the same time, and often do (183). Consequently, there 

 are nerve actions which the vis nervosa of the internal im- 

 pressions produces (353), whether a conception co-operates with 

 it or not. 



361. The following irrefragable truth follows from these 

 two leading principles : while the animal machines are endowed 

 by nature with the property of conducting external impressions 



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