CHAPTER XII. 



THE NERVES AND THEIR FUNCTIONS. 



1. IN describing the nerves and their functions, it will be 

 necessary to classify them, or to reduce them to such arrange- 

 ment, as the present state of our knowledge on the subject 

 will admit. The following comes as near such a classifica- 

 tion as it is possible to make : l\j Nerves of Special Seme. 

 2. Motific Nerves. 3. The Respiratory Nerves. 4. The 

 Regular Nerves, 5. The Ganglionic Nervesf 



2. FIRST ORDER. t-The nerves which contribute to the 

 senses of sight, hearing, and smell, constitute the first class, 

 and are called Nerves of Specific Sense ; Because they are in- 

 capable of communicating any other impressions|fthan such 

 as belong to the respective senses with which they are con- 

 nected. For example, the olfactory can only transmit ideas 

 of odours, the optic of colours, the auditory of vibrations, 

 no matter what the stimulants may be which excite them 

 to action. If we send an electric shock to the eye, it re- 

 ceives the impression of light ; to the ear, of sound ; and to 

 the nose, an odour is perceived : so also, if we press or strike 

 the ball of the eye, we experience a vivid sensation of light, 

 and the same phenomenon occurs when the eye is pierced by 

 the needle of the surgeon : so also, if we take two pieces of 

 different kinds of metal in the mouth, and placing one over, 

 and the other under the tongue allow their edges to come 

 together, we perceive at once a peculiar taste, excited by 

 galvanism. Thus do these nerves communicate to the mind 

 that they are affected in the only manner of which they are 

 capable. 



