io IMMUNE SERA 



ways the alexin necessary to co-operate with the 

 substance sensibilatrice is introduced. This alexin 

 no longer exists in the immune serum, if this be 

 not perfectly fresh, for we have seen that it decom- 

 poses either on warming or spontaneously on 

 standing. A bactericidal serum, therefore, that 

 has stood for some time is incapable of dissolving 

 bacteria. It is possible, however, to make an old 

 inactive serum again capable of dissolving bacteria 

 in vitro by adding ailittle fresh alexin, according 

 to the suggestion of Metchnikoff. In other words, 

 it is thus reactivated. Another obscure point was 

 cleared up by these studies: why a specific bac- 

 tericidal serum which is inactive in vitro should 

 be intensely active in the living body. This is 

 because in the living body the serum finds the alexin 

 necessary for its working, which is not the case in 

 the test-tube unless fresh normal serum be added. 

 We see from all this that even the first experiments 

 in haemolysis have served to clear up a number of 

 practical points in an important branch of bacteri- 

 ology. 



Ehrlich and Morgenroth on the Nature of Haemol- 

 ysis. In continuing the study of hsemolysines we 

 must note particularly the researches of Ehrlich 

 and Morgenroth. These authors asked themselves 

 the following questions: (i) What relation does 

 the haemolytic serum or its two active components 

 bear to the cell to be dissolved? (2) On what 

 does the specificity cf this haemolytic process de- 



