SECT. i. THE NERVOUS SYSTEM. 5 



the animal approaches the higher grades of life, and 

 only attains its perfect development in the human race. 



The bones of man and the higher animals are clothed 

 with a system of muscles, so attached that the head, 

 eyes, limbs, &c., can be moved in various directions. 

 In each of these muscles the fibres of two sets of nerves 

 ramify, namely, the sensory and the motor nerves. 



The sensory nerves convey external impressions to 

 the brain, and by them alone the mind is rendered con- 

 scious of external objects. The impressions made by 

 light and sound upon the eye and the ear, or by me- 

 chanical touch on the body, are conveyed by the sensory 

 nerves to the brain, where they are perceived, though 

 the impressions take place at a distance from it. Con- 

 versely, the mind or will acts through the brain on the 

 motor nerves, which by alternately contracting, relaxing, 

 and directing the muscles, produces muscular motion. 

 Thus the motor nerves convey the emotions of the mind 

 to the external world, and the sensory nerves convey 

 the impressions made by the external world to the mind. 

 By these admirable discoveries, Sir Charles Bell has 

 proved that c we are placed between two worlds, the 

 invisible and the material ; ' our nervous system is 

 the bond of connection. The connection, however, 

 between the mind and the brain is unknown : it has 

 never been explained, and is probably inexplicable; 

 yet it is evident that the mind or will, though im- 

 material, manifests itself by acting on matter ; that is, 

 as a power which stimulates the nerves, the nerve-force 

 acting on the muscles. Mental excitement calls forth 

 the most powerful muscular strength, and an iron will 

 can resist the- greatest nervous excitement. The ner- 

 vous and muscular forces are perpetually called into 

 action, because, for distinct perception, the muscles re- 

 quire to be adjusted. Mind is passive as well as active : 

 we may see an object without perceiving it, and we may 



