522 



NATURE S TEACHINGS. 



to hear any sound more distinctly, we place the open hand 

 behind the ear, so as to enlarge its receptive capacity, and 

 send a greater volume of sound into the ear. 



The well-known experiment of holding a shell to the ear so 

 as to hear the murmur of the sea is due to the same cause, the 

 shell collecting, though in a mixed manner, all the surrounding 

 sounds, and making a murmur which really resembles the 

 distant wash of the waves upon the shore. 



Then, if we examine the various animals which need acute 

 hearing, either to seize prey or escape from enemies, we shall 

 find that they have large and mobile ears, which can be directed 

 so as to catch the expected sound. The hare, rabbit, and deer 

 are examples of the latter, while the former are well repre- 



SAVAGE TAPPING TREE. 



SURGEON USING STETHOSCOPE. 



sented by the domestic cat, whose ears are always pricked 

 forward when she hears the scratchings of a mouse. 



Another most useful appliance is the Stethoscope, which 

 enables the skilful surgeon to investigate the interior of the 

 body almost as clearly as if it were transparent. It is per- 

 fectly simple, being nothing but a trumpet- shaped piece 

 of wood, formed as shown in the illustration. Sometimes 

 it is hollow, and sometimes solid, but the result is the same, 



