THE AUDITORY APPARATUS 131 



consider, if only speculatively, the working of the system 

 in some other sensory circuits. 



Suppose the transmitter at A to be the hand instead of 

 the ear, and the hand to become uncomfortably hot by 

 reason of its proximity to a fire. The heat waves alter 

 the total resistance of the circuit, a message is accordingly 

 transmitted to area a, of the brain, and area c, acts upon it 

 by ordering the voluntary muscles controlling the requisite 

 movement of the arm to withdraw the hand to a safer 

 position. 



Again, we will imagine the transmitter at A to be the eye. 

 The differences of light which form an image or a picture 

 are not transmitted to the brain in exactly the same manner 

 as are sound or heat waves but they are, I am convinced, 

 the result of vibratory differences in resistance and, there- 

 fore, belong to the same category. A speck of dust is, we 

 will say, approaching the eye, the resistance of the circuit 

 is altered and area a, made aware of the fact. Orders are 

 at once passed on to area c, for the eyelid to close, and it 

 closes accordingly. 



Broadly speaking, there are two classes of theories which 

 seek, but do not profess, to explain the working of the 

 auditory apparatus. Few people, I fancy, believe it to be 

 due to chemical reaction. Personally, I would as soon 

 accept the hypothesis that a Leyden jar could be charged 

 by a Seidhtz powder. Concensus of opinion seems to 

 attribute the so-called mechanism of hearing to mechanical 

 vibration but with all respect to the authorities it is not, 

 I submit, the function of any nerve to convey purely 

 mechanical impulses, although excised nerve may respond 

 to mechanical irritation. The two things, however, are 

 not the same. 



At the risk of labouring the point I repeat that the vibra- 

 tions impinging upon the drum of the external ear are 

 mechanical, but as well imagine the line wire of the telephone 

 circuit to vibrate in unison with the diaphragm as to give 

 credence to the statement that the auditory nerves are 

 constantly in mechanical excitement- 



