690 SENSATION. [CH. L. 



giddiness, and consequent muscular efforts to correct it. The 

 results of stimulation, indeed, are precisely analogous to those of 

 extirpation, only in the reverse direction. 



CHAPTER L. 



SENSATION. 



BEFORE passing to the study of the various special senses, 

 there are a number of general considerations in connection with 

 the subject of sensation that demand our attention. 



The psychologist divides the mental phenomena, which the 

 physiologist localises in the brain, into three main categories : 



1. Intellectual : perceiving, remembering, reasoning, ifec. 



2. Emotional : joy, love, hate, anger, &c. 



3. Volitional : purposing, deliberating, doing. 



These are all closely connected together, and are all present in 

 each healthy brain ; but according as one or other may predomi- 

 nate, we speak of intellectual, emotional, or strong-willed indi- 

 viduals. The connection is especially close between intellect and 

 will, which represent as it were the two sides of what we may 

 call a conscious reflex action ; the intellect gives the reason or 

 stimulus for the exercise of the volitional power. The emotions 

 are more complex, and we shall not discuss them ; they are 

 elaborate mental processes, in which sensations predominate. 



The intellectual faculties are derived from the senses; sensa- 

 tions form the materials for intellect ; in other words, we know 

 and learn from what we see, feel, hear, taste, and smell. People 

 born blind or deaf thus labour under the great disadvantage of 

 having one or the other channel of knowledge closed ; they can, 

 however, make up for this in some measure by an education, and 

 consequent increased sensibility of the channels that remain open. 



The simplest mental operation is a sensation that is, the 

 conscious reception on the mind of an impression from the external 

 world. For this the following things are necessary : 



1. A stimulus. 



2. A nerve-ending to receive it. 



3. A path to the brain. 



4. A part of the brain to receive the impulse. 



The brain refers the sensation to the nerve-ending which 

 received the stimulus ; thus pain in the finger is referred to the 



