556 



SENSORY EQUILIBRIUM AND DARK ADAPTATION 



with a decrease in the temperature, as required by the first assump- 

 tion. The velocity constants of the curves drawn for dark adapta- 

 tion show the familiar relation to temperature. The rate of dark 

 adaptation is faster for higher temperatures, the coefficient for 10° 

 being 2.4. The relation of the data to the hypothetical reaction 

 P -\- A ^^ S is perhaps better illustrated by Fig. 3. The points are 

 derived from the averages of Table IV, and the curves represent the 

 theoretical rate of formation of photosensitive substance at the 

 three temperatures according to a reaction of the second order. 



TABLE IV. 



Dark Adaptation at Different Temperatures. 



3. This quantitative agreement of observed values with those pre- 

 dicted on the basis of an hypothetical photosensitive chemical system 

 is convincing proof of the plausibility of the latter. It is my pur- 

 pose, as this work proceeds, to map out in increasingly greater detail 

 the dynamics of this photochemical system, and to test various 

 deductions from it. It is hoped in this way finally to reach a more 

 or less complete statement of the physicochemical nature of the 

 substances and processes that underlie the photosensory responses 

 of an animal like My a. 



SUMMARY. 



1. The reaction time of Mya to light is composed of two parts. 

 The first, a sensitization period, is an exceedingly short interval of 



