DISEASES OF THE BKAIN AND NERVES. 3 



with paralysis only such parts as its ramifications are dispersed 

 upon. 



Again ; Sir Charles Bell has proved to us, by a series of most 

 interesting experiments, and the facts have since received the con- 

 firmation of pathological observation, that there are nerves for sen- 

 sation and nerves for volition of motion ; and that, although for 

 the sake of convenience of distribution the sentient and motor 

 fibrilloe are commonly inclosed within the same tunic, there are 

 instances in which they are altogether separate. We now per- 

 ceive the reason why, in cases of paralysis, sometimes sensation is 

 lost, sometimes only the power of moving the part, at other times, 

 both faculties are gone : all depending upon the injury done to the 

 sentient and motor nerves or to their sources, which latter being the 

 sam.e or very near together, and the nerves themselves being com- 

 monly within the same envelope, accounts for both feeling and 

 motion, ordinarily, being destroyed in paralytic parts. 



We now also know, that no act of volition can take place with- 

 out a previous sensation : — how could my mind give the mandate 

 for extending my arm, unless it were conscious of its being already 

 flexed 1 And by parallel reasoning, morbid actions of parts we shall 

 find to be mostly dependent upon morbid sensations or impressions. 

 Stringhalt, which may be compared to chorea, both being affec- 

 tions in which the will has in a measure lost its controul over the 

 voluntary muscles, may either proceed from something existing in 

 the spine, along the course of the nerves, or in the affected limb 

 itself, or even, for aught I know, in some remote part of the body : 

 the doctrine of " reflex nervous action" has so much enlightened 

 and extended our views of spasmodic and convulsive diseases, that 

 we no longer confine our researches to the brain or spinal marrow, 

 or even to the trunks of the nerves, to discover the source of their 

 origin. 



A most important field of study towards the due understanding 

 of nervous diseases and derangements is presented to us in those 

 new departments of the nervous system, the respiratory of Sir 

 Charles Bell, and excito-motory of Dr. Marshall Hall, which were 

 formerly confounded with others, or rather of whose distinct ex- 

 istence we before possessed no knowledge at all. 



