'^6o i.oc;al tissue reactivity 



potency of Foissinan aiui;^en-|-anlil)0(ly (oniljiualions and will 

 subsequently receive consideration. 



Two more batches of the anti-ral)bit guinea pig" serum with 

 approximately the same precipitating titer as the above described 

 sera were negative by themselves and in combination ^vith rabbit 

 sera. Fresh sera sho^ved more activity than sera stored in the 

 refrigerator for several weeks. It appeared that the reacting fac- 

 tors formed irregularly in combinations of rabbit sera with 

 antisera; or possibly, that with the use of rabbit sera as an anti- 

 gen some individual and as yet unkno\vn factors conditioned the 

 susceptibility of rabl)its to the combination of homologous anti- 

 gen 'with antisera. 



REACTING POTENCY OF AGGEUTINATED RED BEOOD CELLS 



Negative results ^vere obtained by me ^vith mixtures of 5 per 

 cent Group A htunan red blood cells with undiluted A group 

 human serimi, and also ^vith 5 per cent Group B red blood cells 

 with undiluted gioup /i human serum. The mixtures were in- 

 cubated for one hoiu" and ke})t in the refrigerator overnight. 



According to Plant (19,^4) and P. Bordet (19366), sheep red 

 blood cells, sensitized with rabbit anti-sheep hemolytic serum, 

 possessed a strong reacting potency. In the control experiments 

 of P. Bordet, sheep red blood cells and the hemolytic serum gave 

 no reactions w^hen injected separately. It is of interest that reac- 

 tions were also elicited by this latter author with sensitized sheep 

 erythrocytes from Avhich the hemolytic serum ^vas removed by 

 washing. 



TITRATION OF REACTING POTENCY OF PRECIPITATES 



Titrations for reacting potency were carried out ^vith precipi- 

 tates derived from mixtures of anti-meningococcus anti-human 

 horse sera with normal human sera, in proportions of 0.9 c.c. to 

 0.05 c.c, respectively. The precipitates obtained in the manner 

 described previously, gave highly turbid suspensions and had a 

 tendency to settle on the bottom of the test tube. The aggregates 

 were easily broken up by shaking. The dilutions 1:5 and 1:10 of 

 these suspensions ^vere also quite turbid. In dilution 1:50 the tur- 

 bidity was slight and in dilution 1: 100 the fluid ^vas clear. Various 

 dilutions of the suspensions were tested for reacting potency in 

 rabbits prepared ^vith B. typhosus "agar washings" filtrate. The 

 tests were made in the cotirse of the ^veek following the prepara- 



