Dissociation of Microbic Species. 



37 



fluid media. They were found in every case to satisfy these 

 criteria. What is more, the acid agglutination point is distinctly 

 different to that of the D variety. It is in the nature of a physical 

 constant for each type, and is an important differential criterion. 

 All of these characters persist throughout many passages in un- 

 diluted serum, a medium markedly antagonistic to the original 

 change. It cannot be said that the presence of the peptone causes 

 the mutation D G, since the change occasionally occurs, 

 though very rarely and in small amount, in undiluted rabbit serum. 

 On the other hand, the presence of peptone in suitable concentra- 

 tion greatly accelerates a reaction toward which a tendency already 

 exists. It is of interest to note that four pure-line strains, kept 

 on ice in undiluted rabbit serum for three months without passage, 

 showed no evidence of the appearance of G colonies. 



18 (1765) 

 Dissociation of microbic species. 



III. Differentiation of microbes D and G by acid agglutination. 



By PAUL H. DE KRUTF. 



[From the Laboratories of the Rockefeller Institute for 

 Medical Research, New York City.] 



Granular sedimenting growth in liquid medium is one of the 

 principal characters differentiating microbe G (bacillus of rabbit 

 septicemia) from its parent D form. Type G exhibits the granular 

 appearance not only in plain broth, but in serum broth and in 

 undiluted serum as well. This fact led to the examination of the 

 comparative acid flocculation points of the two types. The 

 method used was that of Michaelis, later described in full by 

 Beniasch. 



The suspensions of types G and D were prepared by washing 

 the sediments from 5 per cent, serum broth cultures in large 

 volumes of distilled water. After this procedure had been re- 

 peated four times, the final suspensions were carefully brought to 

 equal turbidity. Prepared in this way, the G type suspension 

 shows a stability equal to that of D. 



The tests for acid agglutinability were carried out with mix- 



