58 IMMUNE SERA 



other infectious disease should not act in a test- 

 tube unless there had first been added some normal 

 serum (according to Metchnikoff), or there had 

 been employed a perfectly fresh serum (according 

 to Bordet) : simply because in either of these 

 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 stand- 

 ing. 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 a little 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 Haemo- 

 lysis. In continuing the study of hsemolysins we 



