S. C. BROOKS 183 



1. The apparent course of photoinactivation is that of a mono- 

 molecular reaction. 



2. Diffusion is not the limiting factor responsible for this fact, 

 because the temperature coefficient of diffusion is much higher than 

 that of photoinactivation (Qio = 1-22 to 1.28, and Qio = 1.10 respec- 

 tively) . 



3. There is no change in the transparency of serum solutions during 

 photoinactivation, at least for light of the effective wave-length, 

 which is in the ultra-violet region probably at about 2530 Angstrom 

 units. 



It is pointed out that under these conditions only one interpre- 

 tation is possible; namely, that during photoinactivation a single 

 disappearing molecular species governs the rate of reaction. This 

 substance must be primarily responsible for the hemolytic power of 

 serum when it is used as complement. 



