104 IMMUNE SERA 



absent entirely in an individual in whom they were 

 previously present. For example, the serum of a 

 dog will at times dissolve the red cells of cats, rab- 

 bits, and guinea pigs, at other times not. Further- 

 more, the serum of one and the same animal may 

 possess specific haemolytic properties for certain 

 cells, and later on may lose this property entirely. 

 In human serum these same individual and periodic 

 variations may be demonstrated, as Wassermann 

 was able to prove experimentally. However, the 

 circumstances on which these variations depend are 

 as yet entirely unknown to us. Possibly we are 

 dealing here with subtle pathological changes. 



Source of the Complements Leucocytes as a 

 Source Other Sources. Where do the comple- 

 ments or alexins originate? This question has been 

 studied particularly by Metchnikoff and by Buch- 

 ner; also by Bail, Hahn, Schattenfroh, and others. 

 These investigators believe that the leucocytes are 

 the source of the complements or alexins. There 

 is, however, this difference between the views 

 of Metchnikoff and Buchner: whereas Buchner 

 believes the alexins to be true secretory products, 

 Metchnikoff believes that they originate on the 

 breaking up of the leucocytes, i.e., that they are de- 

 composition ^products. Metchnikoff bases his belief 

 chiefly on the work of his pupil, Gengou, who showed 

 that although the serum was rich in alexin (i.e., com- 

 plement) the plasma contained none at all. 



