238 PHYSIOLOGY. 



of much improvement by cultivation. The Indian in the 

 forest, accustomed to listen to the approach of his enemies, 

 or of his prey, acquires such acuteness of this sense, as to 

 hear sounds which would be inaudible to those who live amid 

 the din of civilized life. The blind also excel in the acute- 

 ness of hearing, and for this reason especially, acquire great 

 skill in performing on musical instruments. Shakspeare 

 thus describes a person destitute of musical taste. 



" The man that hath no music in his soul, 

 Nor is not moved with concord of sweet sounds, 

 Is fit for treasons, stratagems, and spoils ; 

 The motions of his spirit are dull as night, 

 And his affections dark as Erebus ; 

 Let no such man be trusted." 



Questions. What are sounds ? Describe the external ear ; the 

 tube of the external ear ; the membrana tympani ; the drum, or tym- 

 panum ; the eustachian tube. How many little bones of the ear are 

 there ? Their names and office ? How are low sounds perceived ? 

 What is the use of the spiral passages ? How is sound conveyed ? Is 

 it conveyed by solids ; by water ? What is the stethoscope ? Can 

 sound be propagated from one medium to another ? At what rate does 

 it travel ? How can we tell the distance of sound ? What effect has 

 the density of air on sound ? How is the lengthened peal of thunder 

 explained ? How is hearing performed in the lower order of animals ? 

 Can hearing be improved by cultivation ? 



