4o 



Scientific Proceedings (117). 



It will be observed that the range of C H + at* which the smallest 

 amount of beef infusion is required is for each type precisely the 

 zone of the acid agglutination recorded in the preceding paper. 

 This experiment indicates that the beef infusion, per se, does not 

 cause the agglutination. It merely widens the acid agglutina- 

 tion zone. This would seem to throw light upon the mechanism 

 of the granular growth character of type G in plain broth. 



Suspensions of types D and G were similarly tested against 

 decreasing concentrations of peptone at varying C H +. In these 

 experiments the results were of a different nature, as might have 

 been expected from the failure of peptone to agglutinate type G 

 at P H = 7-5 to P H = 6.8. In the case of peptone, the optimum 

 for type G lies at a range between P H = 3.0 and P H = 2.5. 

 That for D, at Ph = 2.5. Peptone, therefore, seems to shift the 

 optimum zone in the direction of a higher C H +, an effect analogous 

 to that observed in the glycocol-HCl buffer mixtures. In the 

 case of microbe D, strong concentrations of peptone (1-2 and 1-4) 

 actually suppress flocculation completely at Ph — 30. This 

 effect is analogous to the pre-zone phenomenon in immune reac- 

 tions, since for the higher dilutions of peptone at this C H +, com- 

 plete agglutination readily occurs. 



It would appear from the foregoing that while the flocculation 

 in all cases under consideration is due to H-ions, at the same time 

 other factors, such as glycocol, peptone or beef infusion, either 

 shift or broaden the acid agglutination optimum. 



20 (1767) 

 Dissociation of microbic species. 



V. Further considerations in regard to the virulence of 

 microbes D and G. 



By PAUL H. DE KRUIF. 



[From the Laboratories of the Rockefeller Institute for 

 Medical Research, New York City.] 



The wide variations in virulence between microbes D and G, 

 bacillus of rabbit septicemia, has been demonstrated in the first 

 paper of this series. 1 Microbe D, the type found in natural in- 



1 Jour. Exper. Med., 1921, xxxiii, 773. 



