THE EFFECT OF TEMPERATURE ON THE LATENT 



PERIOD IN THE PHOTIC RESPONSE OF 



MYA ARENARIA. 



By SELIG HECHT. 



{From the Physiological Laboratory, College of Medicine, Creighton University, 



Omaha.) 



(Received for publication, May 19, 1919.) 



The purpose of this paper is to present an analysis of the relation 

 between the temperature and the duration of a biological process. 

 The numerous investigations which have already been published 

 (Kanitz, 1915) have demonstrated that biological activities exhibit 

 variations in rate at different temperatures. Usually the speed of 

 the process is an exponential function of the temperature. Occa- 

 sionally the relation between the two is linear. The latter phase 

 has been particularly emphasized by Krogh (1914) and his colleagues. 



However, no matter what the relation between the temperature 

 and the rate may be, it fails to hold at higher temperatures. The 

 rate of increase of the activity falls off decidedly. The velocity of 

 the process soon reaches a maximum at a critical temperature. 

 Above this so called optimum the activity declines or ceases altogether. 



There has been much discussion as to the significance of these 

 variations (Kanitz, 1915), and of the magnitudes of Qio, the tem- 

 perature coefficient for 10°C. On the one hand, the value of the 

 temperature coefficient, as usually found between 2 and 3, has been 

 made to signify that the fundamental process underlying the activity 

 is a chemical reaction. This is because of the well known van't Hoff 

 rule for the relation between the temperature and the velocity of 

 ordinary chemical reactions. On the other hand, much effort has 

 . been spent to show that biological processes do not possess a con- 

 stant temperature coefficient even for temperatures below the opti- 

 mum (Krogh, 1914), and that consequently they do not obey the law 



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