7 8 IMMUNE SERA 



unchanged, no haemolysis taking place. If, how- 

 ever, they added some of this normal horse serum 

 to the centrifuged red cells, the latter immediately 

 dissolved. Now, to the clear centrifuged fluid, 

 which as we have seen would not dissolve rabbit 

 red cells, they added guinea-pig red cells and again 

 some normal horse serum to reactivate the mixture. 

 The guinea-pig red cells all dissolved. This proved 

 conclusively that in the normal goat serum there 

 had existed two specific inter-bodies. One, for 

 rabbit red cells, had been tied by these cells and 

 carried down with them in centrifuging ; the other, 

 specific for guinea-pig red cells, had remained 

 behind. 



Multiplicity of the Active Substances. Further 

 investigation led these authors to assume a still 

 greater multiplicity in the substances in normal 

 serum which are concerned in haemolysis. In 

 addition to the two interbodies just mentioned, they 

 demonstrated the existence in goat serum of two 

 specific complements, one for each interbody, and 

 they were able by means of Pukall filters to separate 

 these two. In this filtration the complement fit- 

 ting the inter-body for rabbit blood remained 

 behind for the greater part, while that fitting 

 the inter-body for guinea-pig blood mostly passed 

 through. 



Whereas then, according to Buchner, only one 

 substance, the alexin, is concerned in the haemo- 



