38 



Scientific Proceedings (117). 



tures of Na lactate-lactic acid, range P H = 47 to P H = 2.4, and 

 with Na acetate-acetic acid, range P H = 5-6 to Ph = 3.2. The 

 mixtures of these buffer series with the microbic suspensions were 

 incubated at 43 0 C. for 16 hours. Readings were taken at the 

 end of this time. A distinct difference in acid agglutination 

 optimum for the two types was observed. The optimum for 

 type G in general occurs at a range between P H = 47 and P H 

 = 4.0. Type D, on the other hand, shows complete sedimenta- 

 tion between P H = 3-5 and P H = 3.0. Many strains of the two 

 types have been examined with invariably the same result. This 

 observation furnishes an important differential criterion for the 

 two varieties. The constancy of the acid agglutination optimum 

 for type D is very strict. That for type G is slightly less so, but 

 the variation is never so great as to cause it to be confused with 

 D. 



19 (1766) 

 Dissociation of microbic species. 



IV. Factors influencing the acid agglutination optimum of 

 types D and G. 



By PAUL H. DE KRUIF. 



[From the Laboratories of the Rockefeller Institute for 

 Medical Research, New York City.] 



It is generally supposed that the acid flocculation optimum of 

 bacteria is referable only to the C H + and is not influenced by the 

 character of the buffer salts or the anion of the acid. This in- 

 terpretation is questionable in the light of the following facts. 

 Microbes D and G were tested against a glycocol-HCl buffer 

 series, range P H = 3.0 to Ph = 1.2. The same suspensions were 

 tested simultaneously with the Na lactate-lactic acid and the 

 Na acetate-acetic acid series employed in the experiments de- 

 scribed in the preceding paper. The results are presented in the 

 following table. 



This experiment indicates that other factors besides the C H + 

 are important in the interpretation of the acid agglutination point 

 of the organisms in question. For example, complete flocculation 

 of type G occurs at Ph = 3.0 in the glycocol HC1 series, while no 



