IMMUNITY. 



237 



charged with sensibilisatrice and alexin but which remains free in the presence 

 of normal corpuscles or of corpuscles merely sensitized — i. e., corpuscles treated 

 with heated serum alone. The absorption of this colloid by corpuscles which 

 have been treated with both sensibilisatrice and alexin has the effect of enegeti- 

 cally agglutinating them and of rendering them more susceptible to hemolysis 

 except under certain circumstances. * * * The absorption of the sensitized 

 and alexinized corpuscles is very likely due to molecular adhesion, the preUmi- 

 nary treatment having modified the corpuscles in so far as their adhesive proper- 

 ties are concerned. Under these conditions the absorption may take place 

 independently of the species of animal from which the corpuscles are obtained, 

 it may even take place with the corpuscles of the same animal which furnishes 

 the colloid, as in the case of. ox serum. 



Now, if the contention of Bordet as set forth above is cor- 

 rect, and if the two bodies concerned in cytolysis do not unite, 

 then of course the theory of complement diversion must fall, 

 since it requires as the first condition the union of amboceptors 

 with complements. Nevertheless, there appears to be as yet 

 no other explanation of the phenomena observed on diluting 

 immune serum. 



W.hile it is true that immune blood-serum differs from normal 

 blood-serum in the matter of its behavior on dilution, this differ- 

 ence is one of degree rather than of kind. For normal blood- 

 serum kills relatively more bacteria when it is diluted than when 

 undiluted.* Normal serum which will kill a given number of 

 bacteria when undiluted will kill a great many more than -^-^ 

 that number when diluted i :io; it will kill a great many more 

 than y^ of the number killed by the undiluted serum when 

 diluted in the proportion of i :iooo. In some cases the normal 

 serum will not only kill relatively more bacteria than the 

 undiluted, but actually more. 



*Bolton. The Bacteriolytic Power of the Blood-serum of Hogs. U. S. De- 

 partment of Agriculture. Bu. An. In. Bulletin No. 95. 



