330 APPLIED PHYSIOLOGY 



there is no external or middle ear, although a bone extends 

 from the inner ear to a kind of drum membrane just under 

 the skin. In the fish there is no external or middle ear, 

 and the labyrinth has no cochlea, but the vibrations are 

 transmitted only through the skull. In the lobster there is 

 a small cavity filled with liquid, in which are the endings 

 of the nerves of hearing. The vibrations producing sound 

 are transmitted to the bag through the sides of its head. 

 Thus all animals which have ears at all, possess what in 

 man is the internal ear. 



SUMMARY 



1. The sense of taste is excited by substances which 



become dissolved in the saliva and excite special 

 nerves in the tongue and pharynx. 



2. The sense of taste enables one to distinguish good 



food from bad. 



3. The sense of smell is excited by minute amounts of 



gas, which excite special nerves in the upper part 

 of the nose. 



4. Smell guards us against foul air and decayed sub- 



stances. 



5. Sound is produced by vibrations of the air. 



6. The inner ear consists of winding canals filled with 



liquid into which special nerves project. Vibra- 

 tions of the air excite the nerves and produce the 

 sense of sound. 



7. The middle ear consists of a bony cavity across which 



three small bones convey the vibrations of the air 

 to the inner ear. 



8. Deafness is often caused by the Eustachian tube being 



stopped. 



