598 MANUAL OF PHYSIOLOGY. 



called the color or timbre of the note. It depends on the number, 

 the variety and the relative intensity of the over-tones or har- 

 monics, which accompany the notes. So that really the timbre 

 or quality of a note, and therefore the special characters of the 

 different musical instruments, is produced by their impurity, or 

 the complexity of the over-tones which aid in producing them. 



All elastic bodies can vibrate, and therefore are more or less 

 capable of conducting sounds. Sound vibrations can be trans- 

 mitted from one body to another placed in contact with it. From 

 a hard material the waves are readily communicated to the air, 

 and this is the ordinary medium by means of which sound is 

 transmitted and finally arrives at our organs of hearing. The 

 old experiment of placing a small bell under the glass of an 

 air-pump and making the tongue strike it after the air has been 

 removed, shows that the medium of the air is essential for the 

 transmission of the sound vibrations. 



The transmission of waves of sound from the air to more dense 

 materials, such as those which surround our auditory nerve ter- 

 minals, takes place with much greater difficulty than that from 

 a solid to the air, and we find a variety of contrivances by which 

 the gentle waves, arriving at the ear by the air, are collected and 

 intensified on their way to the labyrinth. 



But the medium of the air is not necessary in order that sound 

 may reach the internal ear. Nor is the route through the outer 

 canal, and the drum and its membrane, the only one by which 

 the vibrations can arrive at the cochlea. The solid bone which 

 surrounds the labyrinth is in direct communication with all the 

 bones of the head, and the sound can travel along these bones 

 and reach the nerve endings. This can easily be proved by 

 placing the handle of a vibrating tuning-fork against the fore- 

 head or, better still, against the incisor teeth. The sound, 

 although previously hardly audible, at once becomes quite dis- 

 tinct, or even appears loud. 



This direct conduction .through the bones of the head is, under 

 normal conditions, of little use to man ; but attempts have been 

 made, in cases where the ordinary auditory passages were rendered 

 inefficient by disease, to gather the vibrations on a vibrating plate 



