S. C. BROOKS 201 



2. That inactivation of complement by ultra-violet light is accom- 

 panied by a decrease in its surface tension. 



3. That photoinactivation of complement is not a result of any 

 changes in hydrogen ion concentration since these are less than 0.05 

 pH. 



4. That hydrogen ion concentrations high enough to transform 

 serum proteins from the cation to the anion condition {i.e. past the 

 isoelectric point) permanently inactivate complement. 



These facts together with those given in previous papers lead to 

 the following hypotheses. 



1. That there is present in serum a hemolytic substance which is 

 formed from a precursor (which may resemble lecithin) and is con- 

 stantly being formed and simultaneously being broken down into 

 inactive products. 



2. That both precursor and lysin contain the same photosensitive 

 molecular group. 



3. That the lytic substance is dependent for its activity upon the 

 state of the serum proteins. 



