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NERVOUS SENSATION. 355 



though it is riot probable the poor bird underwent any 

 pain after the first operation. 



The Brain not the only Source of Nervous Power. 

 It is evident from the above facts, and especially from 

 the experiment with the pigeon, that we cannot regard 

 the brain as the only center, or source of nervous power, 

 and absolutely essential to animal life, but that we must 

 attribute to the spinal cord no small influence as an inde- 

 pendent power in maintaining the vital functions of the 

 animal. In all the cases of motion, without the influence 

 of the brain, it must be observed that no discretion, or 

 judgment is employed, but merely an irritated action, ex- 

 cited by the power of some stimulus ; the motion indeed 

 is never spontaneous. Thus a decapitated frog will 

 remain at rest unless it is touched, when it will leap 

 away from the irritant. In like manner, in the case above 

 stated, the act of swallowing would not be performed 

 unless the fauces were stimulated by the food or drink ; 

 and even respiratory movements, spontaneous as they 

 may seem to be, would not probably be performed unless 

 the lungs were stimulated by the admission of venous 

 blood. 



It is evident, therefore, that though there may be mus- 

 cular motion without the influence of the brain, still it is 

 performed without the act of the will, and of course with- 

 out the interference of discretion ; but that these motions 

 rather resemble those of an automaton, when its springs 

 are touched. 



Are these Movements performed without Feelings? 

 A question now arises, whether the animal, in the cases 

 above cited, experiences any sensation as the cause of 

 motion, or whether it depends merely on nervous irrita- 

 tion. In answer to this question, it may be stated that 

 persons suffering from an injury of the spinal cord may 

 have no feeling in the lower limbs, and still motion may 

 be excited in these members by tickling the soles of the 

 feet, the patient at the same time, being insensible of the 

 motion or its cause ; the nervous influence which would 

 otherwise have conveyed the impression to the brain, be- 

 ing interrupted by the injury of the spine. 



