CHAPTER XIX. 



THE ORGANS OF SPECIAL SENSE: THE SKIN, THE ORGAN OF 

 THE SENSE OF TOUCH, AND OF HEAT AND COLD; THE 

 TONGUE, THE ORGAN OF THE SENSE OF TASTE ; THE NOSE, 

 THE ORGAN OF THE SENSE OF SMELL; THE EAR, THE 

 ORGAN OF THE SENSE OF HEARING; THE EYE, THE ORGAN 

 OF THE SENSE OF SIGHT. 



OUR sensations are both varied and numerous, and arise from 

 within and from without. Sensations arising from within our- 

 selves, such as feelings of fatigue, hunger, thirst, restlessness, 

 etc., and to which we can assign no particular place, we usually 

 speak of under the name of diffuse or subjective sensations. 

 Sensations produced by impressions made on a definite part of 

 the body, and only excited by some particular influence applied 

 to that part of the body, we usually speak of under the name of 

 special or objective sensations : such are sensations of touch, heat, 

 and cold, of taste and smell, and of sound and light. 



Any portion of the body to which a sensation is thus restricted 

 is called a sensory organ, and of these special sensory organs 

 there are five, viz. : 



The skin, the organ of the sense of touch. 

 The tongue, the organ of the sense of taste. 

 The nose, the organ of the sense of smell. 

 The ear, the organ of the sense of hearing. 

 The eye, the organ of the sense of sight. 



In order to be conscious of any sensation, it is necessary for 

 the end-organ (that is, the sensory organ which receives impres- 

 sions) to be placed in communication with the brain, which is 

 the seat of all sensation. If, for instance, the optic nerve, which 

 is the medium of communication between the visual centre in 

 the brain and the end-organ, the eye, be destroyed, the indi- 



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