TEMPERATURE COEEEIi S. 



Intr oductor ^ : A temperature coefficient derived 

 from the rates of a given process for two different temperatures,, 

 is usually defined as t^e factor "by which the rate for the lower 

 temperature is to v e multiplied in order to ?rire the rate for 

 the upper temperature. While the temperature interval may he 

 any value desired it has been usual to consider an interval of 

 ten decrees centegrade and to derive temperature coefficient on 



the basis of a rise of ten degrees. In some investigations 

 where the increase in the rate of the process with rise of tem- 

 perature is very srreat, however, temperature coefficient for 

 smaller intervals have been used, as temperature coefficients 

 for one decree, two degrees or 5 degrees. 



The temperature coefficient for the rate of any process 

 fo*- a rise of 10 decrees is conventionally represented by the 

 symbol OSX. \ IVhen derived directly from experimental data 

 showing rates at ten degree intervals it is of course the quo- 

 tient of the rate at t i signer temperature by the rate at the 

 lower. 



Temperature coefficients for physiological processes 

 have been much discussed in the literature. The statement oc- 

 curs in numerous papers that the rate of a certain process 

 under consideration does or does not obey the "Vant Hoff-Arr- 

 henlue rule" for chemical reaction velocities with change in 

 temperature, this rule being commonly understood to mean that 

 the reaction velocity is doubled cr trebbled for each rise of 

 10 decrees centegrade. It has been usual for biologists to 

 use this rule as thus understood, tc decide whether a given 



