262 OUTPOSTS OF THE INTELLIGENCE SERVICE 



constant note, its response to the same note is found to be 

 inhibited, but notes of sHghtly higher or lower pitch are readily 

 heard. 



Against this theory are arrayed most psychologists and not a 

 few physiologists and anatomists. They find in it no adequate 

 explanation of certain phenomena, e.g. : 



(1) The parrot has only half a whorl of cochlea, but is able to 

 imitate speech and to whistle musical notes over a fair range, while 

 the guinea-pig, with one and a half whorls more than man, produces 

 only squeaks and grunts. 



(2) The bird has a short basilar membrane, about one-fifth that 

 of the mammal, but has numerous hair cells. These cells are set in 

 the bird in rows of thirty or forty, and in the mammal in rows of 

 four. If equal lengths of membrane vibrate sympathetically to the 

 same note, then as the bird has ten times the number of hair 

 cells stimulated as the mammal, it ought to hear the sound 

 correspondingly louder. This does not appear to be so. 



(3) The fibres of the basilar membrane are not separate struc- 

 tures, but are bound together so that we have to deal with a 

 triangular sheet of membrane with the tension applied across the 

 shorter distance. Such a sheet, as we shall see when we consider 

 the pressure-pattern theory, does vibrate as a differential resonator. 

 As a matter of fact, Helmholtz met this difficulty by calculating 

 that a uniform membrane in which the tension was greater from 

 side to side than longitudinally w^ould answer in the same way as 

 a series of fibres as his theory required. 



Displacement Theory. 



The latest form of this theory is put forward by Sir Thomas 

 Wrightson, an engineer. He is supported by Sir Arthur Keith, 

 the eminent anatomist. He considers that the ear is not a 

 physiological piano played upon by the sound waves, but a 

 delicate spring weighing every phase of a sound wave, simple 

 or compound, and transmitting to the brain a record of every 

 fluctuation of pressure in the endolymph of the scala media. 

 Every variation of pressure transmitted by the stapes to the 

 perilymph is in turn transmitted to the membrane closing the 

 fenestra rotunda. The cochlear system is a closed one, in shape 

 rather like a long-drawn-out, doubled-over hour glass, wath the 

 stapes operating at one end. The only relief for the motion of 

 displacement is at the fenestra rotunda, at the opposite end, 

 whose membrane moves to and fro simultaneously with the 

 stapes. These movements are transmitted to the endolymph 

 enclosed in the tube, the scala media, which ends blindly at the 



