468 THE SENSORIAL FUNCTIONS. 



subsequent application of an exciting cause pro- 

 duces more than the usual effect. One of the most 

 obvious exemplifications 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 tem- 

 perature, 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, depends much on the pre- 

 vious state of the organ by which they are perceived ; 

 any strong impression 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 converse of this 

 is observed when hearing has been suddenly restored 

 in deaf persons, by the operation of perforating the 

 ear-drum.* The sensibility of the auditory nerves, 

 which had not been accessible to impressions of 

 sound, is found to be increased to a morbid degree. 

 This was remarkably exemplified in the case of a 

 gentleman, who for several years had been very 

 deaf, in consequence of the obliteration of the 

 Eustachian tube, so that he could scarcely hear 

 a person speaking in a loud voice close to his ear. 



* See the note in p. 388 of this volume. 



