IMMUNOLOGICAL BEHAVIOR 1 27 



neutralizing potency of an immune anti-typhoid serimi diluted 

 1:10 after it was incubated for several hours in a water bath at 

 37° c. He obtained a striking increase in the netitralizing titer. 



Thus, it is obvious that the native reactivating factors which 

 may be present in the immune sera can be destroyed at a tem- 

 perature {i.e., 37° c. for four hours) which has no destructive 

 effect upon the neutralizing antibodies. The destruction of the 

 factors is, then, coincidental with the considerable increase of the 

 neutralizing potency of an immune serum. The therapeutic effect 

 of sera treated in this manner remains to be determined. 



The immunological significance of the reactivating factors Avar- 

 rants consideration, inasmuch as they appear to be non-specific, 

 widely distributed among various species of animals (i.e., man, 

 horse, rabbit and gtiinea pig) and are capable of displaying the 

 effect in vivo. It is conceivable that they may play an an- 

 tagonistic role if present in therapeutic immune sera, i.e., inter- 

 fering both with the effect of passively acquired antibodies and 

 also, possibly, restoring toxicity to toxic substances neutralized by 

 actively acquired antibodies. 



The possible reactivating effect of normal human blood sera 

 {i.e., about 53 per cent of sera tested) should also be taken into 

 consideration in performing blood transfusions in cases of in- 

 fectious diseases. 



Follo^ving the observations on the reactivating factors just 

 described, Michelazzi (1933/-') studied the effect of normal sera 

 upon completely neutralized diphtheria toxin -^antitoxin mix- 

 tures. In these experiments he observed that not infrequently the 

 iyi vitro addition of normal serum to the completely neutralized 

 mixtures may restore the specific toxic effects of diphtheria toxin. 

 Local and general pathological effects specific for diphtheria toxin 

 may be obtained following the injection of completely neutralized 

 diphtheria toxin-(-antitoxin mixtures if the guinea pigs are pre- 

 viotisly treated by injections of normal horse serum. The effect is, 

 ho^vexer, more pronounced if a serum containing anti-horse anti- 

 bodies is used for the reactivation. 



RECAPITULATION 



Unquestionable proof is offered that skin-preparatory and re- 

 acting factors derived from a large group of bacteria are antigenic 

 substances Avhich may be specifically neutralized l)v iiimume sera. 



