S. C. BROOKS 197 



rapid rate it is easy to see that as A is changed to a the concentra- 

 tion of a will increase; later as A is used up a will decrease again. 

 Similarly b and 6' will appear, increase, and disappear. If b' is hemo- 

 lytic there will be a "wave" of hemolytic power in addition to that 

 due to B' and not only the average time curve of photoinactivation, 

 but also the divergence of individual curves from this average is satis- 

 factorily accounted for. The time at which this wave occurs in the 

 course of the process will depend on the rate of the slower of the proc- 

 esses, a to b and b to b'; presumably this is a to & which may well be 

 dependent on an enzyme whose concentration is different in differ- 

 ent samples of serum. If the conditions are favorable we may 

 expect the wave of excess hemolytic power to be so large and so early 

 that the complement becomes more efficient when radiated, as during 

 the early part of Experiment 69 of the preceding paper.22 



In order to render this hypothesis more tangible it is desirable to 

 suggest the nature of the substances A, B, a, b, and so on, even if 

 there is no direct evidence for their exact composition. There is 

 considerable evidence that fatty acids are important in immune 

 reactions : Warden^^ has synthesized from fatty acids antigens which 

 produce specific antibodies against blood cells and gonococcus; Job- 

 ling and BulP* have shown that the lipase content and hemolytic 

 power of human sera vary together. Noguchi," among others, has 

 shown striking analogies between complement and solutions of fatty 

 acid compounds dissolved in serum albumin solutions. All these facts 

 suggest the presence of a fatty acid compound acting as hemolysin 

 in complement. 



The most active hemolysin of which the writer has found any record 

 is the "lysocithin" produced by the action of cobra venom upon 

 crude lecithin and studied by Fourneau and his students. It appears 

 to be at least 50 times as active as saponin and perhaps 100 times as 

 active as the most hemolytic soaps. It is a fatty acid compound: 

 choline monopalmitoglycerophosphate.^^ It should be noted that 



22 Brooks, S. C, /. Gen. Physiol, 1920-21, iii, 180, Table IV; and 181, upper 

 curve of Fig. 2. 



23 Warden, C. C, /. Infect. Dis., 1918, xxiii, 504. 



24 Jobling, J. W., and Bull, C. G., /. Exp. Med., 1913, xviii, 61. 

 2^ Noguchi, H., Biochem. Z., 1907, vi, 327. 



2" Fourneau, E., and Delezenne, C, Bull. Soc. Chim., 1914, series 4, xv, 354. 



