vni THE SPECIAL SENSES 343 



thoughts, under the common head of states of 

 consciousness. But what consciousness is we know 

 not ; and how it is that anything so remarkable as a state 

 of consciousness comes about as the result of irritating 

 nervous tissue, is just as unaccountable as any other ulti- 

 mate fact of nature. 



Sensations are of very various degrees of definiteness. 

 Some arise within ourselves, we know not how or where, 

 and remain vague and undefinable. Such are the sensa- 

 tions of uncomfortahleness, of faintness, of fatigue, or of 

 restlessness. ' We cannot assign any particular place to 

 these sensations, which are very probably the result of 

 affections of the afferent nerves in general brought about 

 by the state of the blood, or that of the tissues in which 

 they are distributed. And however real these sensations 

 may be, and however largely they enter into the sum 

 of our pleasures and pains, they tell us absolutely nothing 

 of the external world. They are not only diffuse, but they 

 are also subjective sensations. 



3. The Special Senses. — In the case of other sen- 

 sations, each feeling arises out of changes taking place in 

 a definite part of the body, is produced by a stimulus 

 applied to that part of the body, and cannot be produced 

 by stimuli applied to other parts of the body. Thus the 

 sensations of taste and smell are confined to certain 

 regions of the mucous membrane of the mouth and nasal 

 cavities ; those of sight and hearing to the particular 

 parts of the body called the eye and the ear : and those of 

 touch, though arising over a much wider area than 

 the others, are nevertheless restricted to the skin and to 

 some portions of the membranes lining the internal cavities 

 of the body. Any portion of the body to which a sen- 

 sation is thus restricted is called a sense-organ. 



It may be here remarked that in the case of the sensa- 

 tion of touch, the simple feeling of contact is accompanied 

 by information, not only as to what sense-organ, but also 

 as to what part of that sense-organ, is being affected. 



