526 THE SENSORIAL FUNCTIONS. 



Other hand, the absence or diminution of the 

 usual excitement leads to a gradual increase of 

 sensibility, so that the subsequent application of 

 an exciting cause produces more than the usual 

 effect. One of the most obvious exemplifica- 

 tions of this law presents itself in the case of the 

 sensations of temperature. The very same body 

 may appear warm to the touch at one time, and 

 cold at another, (although its real temperature has 

 not varied,) according to the state of the organ 

 induced by previous impressions : and a very 

 different judgment will be formed of its tempe- 

 rature, when felt by each hand in succession, 

 if the one has immediately before been exposed 

 to cold, while the other has retained its natural 

 warmth. Similar phenomena may be observed 

 with regard to all the other senses ; thus the 

 flavour of odorous, as well as sapid bodies, de- 

 pends much on the previous state of the organ 

 by which they are perceived ; any strong im- 

 pression of taste made on the nerves of the 

 tongue, rendering them, for some time, nearly 

 insensible to weaker tastes. Sounds, which 

 make a powerful impression on the auditory 

 nerves, will, in like manner, occasion temporary 

 deafness with regard to faint sounds. The con- 

 verse of this is observed when hearing has been 

 suddenly restored in deaf persons, by the opera- 

 tion of perforating the ear-drum.* The sensi- 



* See the note in p. 434 of this volume. 



