422 PROPERTIES AND FUNCTIONS 



They are always contiguous. The sense of smelling may 

 become perverted as well as that of tasting. Odors that 

 were originally unpleasant to us, may by habitual use 

 become not only agreeable but apparently necessary. The 

 nervous papillae may be so changed that the same mate- 

 rial presented at different times may produce entirely 

 different impressions, or they may lose their natural irri- 

 tability so much as not to be easily excited. 



The senses of hearing and seeing are more refined 

 than those of feeling, tasting, or smelling ; and the organs 

 in which the former reside, or.through which the impres- 

 sions are conveyed, are far more complicated in their 

 structure than those of the latter. 



The organ of hearing in men, and the most perfect 

 animals, is the ear. In these there are two distinct open- 

 ings into the ear, a larger or external, (which is surround- 

 ed by a lobe so constructed as in the best manner possi- 

 ble to collect the undulation of the air produced by 

 sonorous bodies, and convey the same to the nerves situ- 

 ated in the internal ear, which convey the impression of 

 sound to the brain,) and an internal opening which passes 

 from the mouth into the ear, and which is called the 

 Eustachion tube. When a person is desirous of hearing, 

 and the sound is imperfect, the mouth is involuntarily 

 opened, and the sound is thus conveyed through this 

 tube. Frogs, and most amphibious animals have no ex- 

 ternal ear, but they hear by means of the internal pass- 

 age or that from the mouth. Among serpents the com- 

 mon harmless snake or blind worm is the only one that 

 has an aperture which leads to the internal ear, that can 

 be discovered. All others have the internal organs de- 

 veloped in an imperfect manner ; and it is therefore pro- 

 bable, at least, that there is some effective entrance to 

 them. The whole cetaceous tribe hear through their nos- 

 trils or blow-holes. ;; *** 



Among fishes, the shark and a few others have the ru- 

 diments of an external ear ; but most of the tribe hear 

 through the external opening alone. Insects have the 

 sense of hearing ; but it is questionable by what organ it 

 is performed. Some have supposed that the antennae 

 performed this office in combination with several other 



