S. C. BROOKS 179 



in the experiments about to be described, more than 95 per cent of 

 the incident Hght of the effective frequency is absorbed by the serum 

 solution. 



The time curves of complement photoinactivation which are given 

 in the following section are therefore susceptible to analysis in terms 

 of chemical kinetics; if the process follows the course of any simple 

 chemical reaction it may be interpreted in terms of the number of 

 kinds of molecules participating in the reaction. 



V. 



The course of complement photoinactivation was determined by 

 radiating a number of portions of the same lot of complement for 

 different periods of time, and plotting their efficiencies as ordinates 

 against their respective periods of exposure as abscissas. The curve 

 connecting these points is assumed to represent the progressive 

 change in efficiency which would occur in a single sample of comple- 

 ment. It was important that there should be no doubt about the 

 fact that the amount of light action was characteristic of the particular 

 serum used, and not simply an amount which might vary according 

 to accidental differences between dift"erent exposures. To establish 

 the fact that a given exposure would always cause the same amount 

 of injury to a given complement solution three portions of comple- 

 ment were exposed for 10 minutes each, and then titrated. Their 

 efficiencies were found to be 56.8, 54.4, and 54.7 per cent respectively; 

 the mean efficiency was 55.3 per cent and the probable error of a 

 single determination was 0.87 per cent which is 1.6 per cent of the 

 mean value. This may be attributed entirely- to errors in titration. 

 Further examples of constant amounts of injury caused by short 

 equal exposures may be found in Table III above. 



Table IV and Fig. 2 present the course followed by the process of 

 photoinactivation of eight different sera. They include all the depend- 

 able data obtained, a large number of the earher experiments having 

 to be discarded because of the difficulty of so arranging the titration 

 as to include for each partially inactivated sample just those dilutions 

 needed to yield a complete "titration curve." While it is probable 

 that other types of inactivation curves might be encountered in the 



