S. C. BROOKS 



173 



their value as higher temperatures are approached it would be prema- 

 ture to assume that such an increase would always be found. The 

 mean value of Qio is 1.10 and may be considered to be typical of the 

 reaction. It is exactly that found in a preliminary experiment 

 in which the rates of photoinactivation at 2 and] at 38°C. were 

 determined. 



70 r 



60 



D 



o 



50 



V40 



o 



30 



20 



10 



10 15 



Radiation 



20min. 



Fig. 1. Courses of the process of photoinactivation of complement at 0, 10, 20, 

 30, and 40°C. The ordinates represent efficiency in per cent of that of unradi- 

 ated complement subjected to the same temperature conditions; and the abscissae 

 represent the time of exposure to light in minutes. 



This value of the temperature coefficient for the process of photo- 

 inactivation is of particular significance because it is such as to allow 

 us to neglect diffusion as a factor of any importance in determining 

 the course of the reaction. For if diffusion were a limiting factor 

 in the reaction the temperature coefficient of photoinactivation should 

 be that of diffusion; i.e., Qio = 1.28. Instead of this it is 1.1 which 

 is about the value which is to be expected in a photochemical reaction. 



