IMMUNOLOGICAL BEHAVIOR 1 25 



2. Rabljits were also treated iiitia\enoiisly with various 

 amounts of the rabbit serum and tested \vith a constant amount 

 of neutralized reacting factors. In this manner, a dose as small as 

 1 c.c. of diliuion 1:50 of the serum ^vas shown to possess the reac- 

 tivating property. 



In one experiment the reac ti\ating effect of the serum persisted 

 for t^ventv-three and one-half hours. Longer periods of time ^vere 

 not studied. 



In further experiments it ^vas also determined whether the 

 rabbit serum added to the neutralized factors /// lutro would dis- 

 play the above described reactivating property. 



One hundred meningococcus reacting units completely neu- 

 tralized as above Avere mixed with rabbit Serum I luidiluted and 

 diluted 1:10 and 1:50, respectively. Each mixture ^vas tested in a 

 group of three rabbits. The ralolDit serum undiluted and diluted 

 1:10 reactivated the neiUralized mixture, inasmuch as all the 

 rabbits tested sho\ved reactions. The dilution 1:50 had no effect, 

 since no reactions were obtained in the group. 



By the use of the above methods there Avas also determined the 

 frequency Avith Avhich the reactivating property occurs in sera of 

 various animal species. The results are summarized in Table vn. 



Table vii 

 TESTING OF VARIOUS SERA FOR REACTIVATING PROPERTY 



As is seen from Table vn, the reactivating property described 

 was found in sera of man, horse, rabbit and guinea pig. About 72 

 per cent of rabbit and 53 per cent of human sera shoAved this 



