THE SPECIAL SENSES. 177 



CHAPTER X. 



THE SPECIAL SENSES. 



The Production of Sensations Variety of Sensations General Sensi- 

 bility Pain and its Function Special Sensation, Touch, Taste, 

 Smell, Sight, and Hearing The Hand, the Organ of Touch TJie 

 Sense of Touch Delicacy of Touch Sensation of Temperature and 

 Weight TJie Tongue the Organ of Taste TJie Nerves of Taste 

 The Sense of Taste and its Relations with tJie oilier Senses TJie 

 Influence of Education on the Taste The Nasal Cavities, or the 

 organs of Smell TJie Olfactory Nerve The Uses of the Sense of 

 Smell The Sense of Sight Light The Optic Nerve TJie 

 Eyeball and its Coverings The Function of the Iris The 

 Sclerotic, Choroid, and Retina The Tears and their Func- 

 tion The Movements of the Eyeball The Function of Ac- 

 commodation The Sense of Hearing and Sound The Ear, or 

 the organ of Hearing The External, Middle, and Internal Ear. 



1. Production of Sensations. We have already 

 seen that the true centre of sensation is some organ within 

 the skull, probably among the gray masses at the base of 

 the brain; but the mind never perceives impressions at 

 that point ; but, on the contrary, always refers them to the 

 external organs of sensation. Hence, it is convenient to 

 say, that those outer parts possess the property of sensibil- 

 ity. For instance, we say that we hear with the ear, taste 

 with the tongue, and feel with the fingers. That this is 

 not the exact truth is proven by the fact, that whenever 

 the nerve connecting one of these organs with the brain is 

 severed, it at once loses its capacity for sensation. 



2. Consciousness, another facujty of the brain, is neces- 

 sary to complete a sensation. During sleep, and in other 

 unconscious states, the usual impressions are presented to 



1 . True centre of sensation ? Place of the mind's impressions ? What is it 

 convenient to say ? What further is stated ? 



2. Consciousness ? During sleep? In profound insensibility ? 



S* 



