13C FUNCTIONS OF THE NERVOUS POWER. 



there, by means of the sensorial power, are recognised 

 by the mind, or to use the popular phraseology, become 

 sensations. 



Emily. But how is it known so certainly that the 

 impression is conveyed to the brain by the nerve solely ? 

 I should like to be acquainted with the grounds of this 

 doctrine. 



Dr. JB. It is demonstrated by the fact abundantly 

 established by experiment and observation, that if the 

 nerve be injured, no sensation is produced in the mind. 

 If the optic nerve, by which impressions made on the 

 organs of vision are communicated to the brain, be in- 

 jured in any way, no object will be perceived, though 

 its image may fall on the retina just as distinctly as be- 

 fore. 



Emily. I do not perfectly understand how sensa- 

 tions are experienced in the brain ; I have always con- 

 sidered their seat to be in the extremities of the nerves, 

 or the organs of sense themselves. Surely, if I grasp a 

 warm body with my hand, I feel the warmth in my fin- 

 gers, not in my brain ; if a wound be made in my arm, 

 I feel the pain in the wound, not in the brain. 



Dr. B. There is a very obvious distinction be- 

 tween sensations and impressions ; the latter are the 

 changes produced in the extremities of the nerve ; the 

 former, the changes produced in the brain and commu- 

 nicated to the mind. The mind however, is accusto- 

 med to refer the seat of its sensations to the seat of the 

 impressions, which circumstance must be borne in mind, 

 or we shall fall into an error. But we are anticipating 

 this part of our subject, for sensation is an effect of the 

 sensorial power, and we have not yet finished our ex- 

 amination of the nervous power. 



Another function of the nervous power is to transmit 

 to the voluntary muscles the stimulus necessary for their 

 action. When I wish to grasp the object before me, 

 the muscles must receive their proper stimulus before 

 they can be put into action. This is conveyed .from the 



