Log ^Intensity 

 Fig. 4 (C) 



Fig. 4. The frequency of nerve impulses in sensory neurons as a 

 function of the intensity of the stimulus. (A) Response of a primary 

 stretch-sensitive neuron in the frog toe to loading.'® (B) Impulse 

 frequency in a primary salt receptor neuron of a blowfly when 

 challenged with various concentrations of aqueous sodium 

 chloride.'* (C) the response of a se cond-ord er^sensory neuron, the 

 eccentric cell, in the compound eye of Limulus to white light of 

 different intensities : (i) steady-response phase, (2) initial phase of 

 response. (A from Matthews,^' Fig. 7; B from Gillary,'* Fig. 3; 

 C from Hartline and Graham,** Fig 6.) 



adequate stimulus (tension) increases logarithmically with incre- 

 ments in length, and therefore the linear increase in impulse 

 frequency with length may represent the usual logarithmic 

 stimulus-response relationship. In any case, it is clear that 

 the mere presence of a logarithmic stimulus transformation in 

 different sense organs should not be taken to indicate a common 

 mechanism of stimulus transduction. 



In addition to the difficulties involved in arriving at an adequate 

 definition of stimulus utilization energy, there are also uncertain- 

 ties in the measurement of response magnitude. Now the output 

 of most receptors is a function not only of absolute stimulus 



15 



