6 NER VE FORCE. PART m. 



hear a sound without attending to it. We must look in 

 order to see, listen in order to hear, and handle in order 

 to feel ; that is, we must adjust the muscular apparatus 

 of all our senses, of our eyes, ears, &c., if we would have 

 a distinct perception of external exciting objects : and 

 that is accomplished by the power of mind acting upon 

 matter. 



Dr. Carpenter has shown that it is by a series of 

 forces acting upon matter that man conveys his ideas to 

 man, the sonorous undulations of the atmosphere being 

 the medium between the two. On one side the will, or 

 power of mind, acts upon the nerves, nerve-force acts 

 upon the muscles of speech, and these muscles, while 

 in the act of speaking, produce sonorous undulations 

 in the atmosphere. On the other side, these undula- 

 tions are communicated by the mechanism of the ear to 

 the auditory nerves, exciting nerve-force, and nerve-force 

 acts upon the mind of the hearer. ' Thus the conscious- 

 ness of the speaker acts upon the consciousness of the 

 hearer by a well-connected series of powers.' 



Nerve-force generates, directly or indirectly, light, 

 heat, chemical power, and electricity. When the optic 

 nerve is pressed in the dark, a luminous ring is seen 

 round the eye, and a blow on the face excites a flash of 

 light. Nervous excitement, by accelerating respiration, 

 increases the chemical combination of the oxygen of 

 the air with the carbon of the blood, and thus produces 

 animal heat. But the development of electricity by 

 nervous and muscular force, is one of the most unex- 

 pected and singular results of physiological research. 



MM. Matteucci and Du Bois E-eymond have proved 

 that the intensity of the nervous and muscular forces 

 is at a maximum when the muscles are contracted ; and 

 that if each arm of a man be put in contact with a wire 

 of a galvanometer so as to form an electric circuit, an 

 instantaneous deviation of the needle will take place, 



