SELIG HECHT 669 



edge it is impossible to apply the mathematical reasoning which 

 is a prime essential for the proper comprehension of the data. The 

 general idea, however, is a decidedly fruitful one; and, though arrived 

 at independently, the analysis to be given in the present paper is 

 really a quantitative application of just such a conception as de- 

 veloped by Putter. The same idea has already shown its possibili- 

 ties in the investigations of Tammann (1895) and of Duclaux (1899) 

 on the effect of temperature on the activity of enzymes. 



The case to be considered is the photic sensitivity of the mollusk 

 Mya arenaria. Previous v/ork (Hecht, 1919, a, h) has enabled us to 

 propose an hypothesis to account for the photic behavior of this 

 animal. The essential value of this hypothesis is its assumption of 

 definite chemical reactions, the dynamics of which are known, and the 

 interrelations of which are given. The effect of temperature on the 

 photic behavior of Mya should therefore permit of a quantitative 

 analysis in terms of the suggested hypothesis. The success of this 

 analysis will then reciprocally furnish justification for the acceptance 

 of the hypothesis. 



11. 



Mya responds to illumination by a rapid retraction of its siphons. 

 Its reaction time is composed of two parts. The first is a sensitiza- 

 tion period. This is the smallest interval of time during which the 

 animal must remain exposed to the light in order to respond at the 

 end of the usual reaction time. The second is a latent period during 

 which Mya may remain in the dark. At the end of this period, the 

 organism retracts its siphons exactly as if it had been exposed for the 

 entire reaction time. 



The sensitization period represents the duration of a photochemical 

 reaction. This has been shown (Hecht, 1919, a) to consist of the 

 decomposition of a photosensitive substance {S) into its two pre- 

 cursors (P and A), according to the reversible system 



light 

 S ^ P + A. (1) 

 "dark" 



