v THE SENSE OF HEAEING 203 



of action by incising or perforating it with a cautery, or when 

 the articulations of the ossicles have lost all their mobility by 

 desiccation, or when the thread is attached to some other point of 

 the temporal bone. But if the tympanic apparatus is thrown into 

 vibration by stronger sound-waves, e.g. from a tuning-fork, instead 

 of by the low ticking of a watch, the anatomical preparation will 

 vibrate in all its parts, and the thread carries the sound-waves to 

 the observer's ear even if it be applied to some point of the bone 

 beyond the chain, or to the chain, even when the tympanic mem- 

 brane is freely perforated, or the chain immobilised or anchylosed 

 by desiccation. In such cases the general vibration of the bones 

 conceals the functional importance of the tympanic apparatus. 



The above experiments as a whole give direct proof that the 

 tympanic membrane with the chain of ossicles is capable of 

 vibrating and transmitting sound-waves of different pitch and 

 minimal intensity. It is therefore more delicate than any human 

 invention to facilitate the propagation of sound-waves. Marvellous 

 as are these artificial instruments no telephone, microphone, or 

 gramophone exists that is capable of receiving, transmitting, or 

 reproducing the tick of a watch at several metres' distance, or 

 whispered conversation, or the innumerable sounds and tones of 

 lower intensity by which we are surrounded, all of which are 

 conducted to the labyrinth of the tympanic system. 



What is the mechanical explanation of this fact ? How is the 

 tympanic membrane capable of vibrating in consonance with the 

 different tones of the musical scale, and of reproducing and trans- 

 mitting the irregular vibrations of even the lowest sounds ? It is 

 obvious that the tympanic membrane behaves quite differently from 

 membranes distended in one place only. When any such mem- 

 brane, as a drum, is struck it gives out a definite note, the pitch 

 of which falls when the size of the membrane is increased, and 

 rises with increase of its tension. When a tone is produced near 

 it, in which the number of vibrations coincides with, or is a 

 multiple of, those of its proper tone, it vibrates by influence. But 

 if the tone produced is of different pitch from that to which the 

 membrane is tuned, its secondary vibrations cease, and it remains 

 at rest. If the same happened with the tympanic membrane, 

 if it vibrated strongly when the vibrations of the external tone 

 coincided with or were a multiple of those of its proper tone, 

 and little or not at all when the external tone deviated from its 

 proper tone, there would then be an enormous inequality in the 

 auditory perceptions, and the functions of the cochlea would be 

 seriously affected, particularly from the musical point of view. It 

 is evident that conditions exist in the tympanic apparatus which 

 render it capable not only of vibrating to the different notes of 

 the scale, but also of reinforcing every kind of regular or irregular 

 periodic vibration ; in other words, the tympanum functions as a 



