THE MECHANISM OF COMPLEMENT ACTION. 



By S. C. brooks.* 



(From the Harvard School of Tropical Medicine, Boston.) 



(Received for publication, August 29, 1920.) 



It has been shown in the preceding paper that the hemolytic action 

 of serum is to be attributed primarily to a single substance which is 

 destroyed under the influence of ultra-violet light by a monomolecular 

 reaction. This fact immediately raises the question of the nature of 

 the photosensitive substance, and leads the writer to make some 

 suggestions as to what such a substance might be.^ 



Certain experiments of the writer seem definitely to exclude the 

 possibility that the serum proteins are primarily responsible for the 

 power of serum to act as complement in specific serum hemolysis, for 

 this power can be abolished by the action of light without producing 

 the sensitization to heat which is characteristic of the effect of light 

 on serum proteins. These experiments, which are summarized in 

 Table I, show that radiated complement is not thereby made more 

 susceptible to injury by heating.^ 



If the rates of heat inactivation of any individual serum before 

 and after radiation are compared, it will be noted that the differences 

 of efficiency are so small as to be attributable to errors in titration; 



* The experiments upon which this paper is based were done by the writer as 

 Research Fellow in the Harvard School of Tropical Medicine. 



^ In this paper the word "complement" will be used to denote any solution of 

 serum used as one component in specific serum hemolysis (the other component 

 being amboceptor); while that particular ingredient of serum primarily respon- 

 sible for its hemolytic power is designated as the "lytic substance" or "lytic 

 principle." 



^ All three experiments were done before the development of dependable meth- 

 ods of titrating complement, and a probable error of about ±3 per cent is to 

 be expected. 



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