5*28 THE SENSORIAL FUNCTIONS. 



loudness of the sounds ; and it was several weeks 

 before this excessive sensibility of the auditory 

 nerves wore off: by degrees, however, they ac- 

 commodated themselves to their proper function, 

 and became adapted to the ordinary impressions 

 of sound. Some time afterwards, this gentleman 

 had a similar operation performed on the other ear, 

 and with precisely the same results ; the same 

 degree of excessive sensibility to sounds was ma- 

 nifested on the restoration of hearing in this ear 

 as had occurred in the first ; and an equal time 

 elapsed before it was brought into its natural 

 state. 



The most striking illustrations of the extent 

 of this law are furnished by the sense of vision. 

 On entering a dark chamber, after having been 

 for some time exposed to the glare of a bright 

 sunshine, we feel as if we were blind ; for the 

 retina, having been exhausted by the action of a 

 strong light, is insensible to the weaker impres- 

 sions which it then receives. It might be sup- 

 posed that the contraction of the pupil, which 

 takes place on exposure to a strong light, and, of 

 course, greatly reduces the quantity admitted to 

 the retina, is a cause adequate to account for 

 this phenomenon : but careful observation will 

 show that the pupil very rapidly enlarges to its 

 full expansion when not acted upon by light; 

 while the insensibility of the retina continues 

 for a much longer time. It regains its usual 



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