On Immunity loith Special Reference to Cell Life. 443 



the facts of bacteriolysis as elicited by the work of PfeifFer, Metchni- 

 koff, and Bordet. In the work on the Pfeiffer phenomenon of bacteri- 

 olysis, it had already been ascertained that the solution of bacteria 

 by specific bacteriolysines was brought about by the combined action 

 of two different bodies : one which was specific, arose during the im- 

 munisation and was stable j and another, a very unstable body, which 

 was present in normal serum. 



In collaboration with Dr. Morgenroth, I have sought in regard to 

 this question, for which haemolysis offered prospects favourable to 

 experimentation, to make clear the mechanism concerned in the action 

 of these two components — the stable, which may be designated " im- 

 mime body," and the unstable, which may be designated "comple- 

 ment" — which, acting together, eff'ect the solution of the red blood 

 corpuscles. For this purpose, in the first place, solutions containing 

 either only the " immune body " or only the " complement " were 

 brought in contact with suitable blood corpuscles, and after sepa- 

 ration of the fluid" and the corpuscles by centrifugalising, we investi- 

 gated whether these substances had been taken up by the red blood 

 corpuscles or remained behind in the fluid. The proof of its location 

 in the one position or in the other was readily forthcoming, since to 

 restore to the hsemolysine its former activity, it was only necessary to 

 add to the " immune body " a fresh supply of " complement," or to 

 the "complement" afresh supply of "immune body," in order that 

 the presence of the hsemolysine in its integrity might be shown by 

 the occurrence of solution of the blood-cells. 



The experiments proved that, after centrifugalising, the " immune 

 body " is quantitatively bound to the red blood corpuscles, and that the 

 " complement," on the contrary, remains entirely behind in the fluid. 

 The presence of the two components in contact with blood cor- 

 puscles only occasions the solution of these at higher temperatures, and 

 not at O^C. And an active hsemolytic serum (with "immune body" 

 and " complement " both present) having been placed in contact with 

 red blood corpuscles and maintained for a while at 0° C, it was found 

 after centrifugalising that, under these circumstances also, the " immune 

 body " had united with the red blood corpuscles, but that the " com- 

 plement " remained in the serum. This experiment showed that both 

 components must, at a temperature of 0° C, have existed alongside of 

 one another in a free condition. 



But when analogous experiments were undertaken at a higher tem- 

 perature it was found that both components wfere retained in the 

 sediment. 



These facts can only be explained by making certain assumptions re- 

 garding the constitution of the two components, i.e., of the "immune 

 body" and the "complement." In the first place, two haptophore 

 groups must be ascribed to the " immune body," one having a great 



