SOUND RECEPTION 101 



air and to sounds of adequate intensity over a wide frequency range; 

 that is, the response is not resonance. As Pumphrey and Rawdon- 

 Smith(1936a, 1936b, 1936c) showed, these hairs are pure displacement 

 receptors sensitive up to about 3,000 c/s. Threshold measurements over 



Frequency Q^/sec) 



Fig. 68. Experimentally determined thresholds of the cercus of Gryllus 

 for pure tones at various frequencies (solid circles). The heavy line 

 represents a constant displacement amplitude of 560 A. The light line 

 represents the human threshold of hearing from Wegel's data. 

 (Redrawn from Pumphrey, 1940.) 



the frequency range 50 c/s to + 1 ,000 c/s (Fig. 69) reveal that the res- 

 ponse is to a constant displacement amplitude of 560 A. (Pumphrey, 

 1940). If the hair acts as a rigid lever this finding suggests that 

 the threshold displacement of the dendrite at the base of the hair 

 cannot greatly exceed 0-5 A. Pumphrey (1940) suggested that the 



