36 



Scientific Proceedings (117). 



It was considered probable that filtrates from D cultures might 

 hasten the D G transformation. Accordingly, cultures of 6, 

 24, 48, and 72 hours were filtered through Berkefeld candles. 

 After sterility had been proved, 0.05 c.c. of pure-line strain B-D 2 

 was seeded into 10 c.c. of each of the above filtrates, into controls 

 of sterile broth, and into undiluted rabbit serum. The tubes 

 were incubated at 37 0 C. and streaked on serum agar plates at 

 intervals up to 176 hours. Contrary to expectation, the number of 

 G colonies arising in the 6- and 24-hour filtrates was extremely 

 small, and comparatively few appeared in that of 48 hours. In 

 the 72-hour filtrate G colonies appeared at a rate and in a con- 

 centration approximately parallel to that of the control broth. 

 The mutation had reached 50 per cent, in 176 hours. In the 

 undiluted rabbit serum no G colonies appeared at any time during 

 the experiment. It would seem, then, that early filtrates from D 

 cultures are antagonistic to the D — G mutation. 



The C H + of the broth seems, within limits, to have no effect 

 upon the rapidity of the mutation. If anything, an acidity > P H 

 = 7.0 retards the process. Tests were made down to Ph = 6.0, 

 beyond which point it is difficult to obtain growth. 



An effort was made to discover the constituents of plain broth 

 that encourage the tendency of? type D to change to the G variety. 

 Pure-line strains of the former were planted in beef infusion, and 

 in various concentrations of peptone (Fairchild). The P H of all 

 the media was adjusted to 7.4. It was found that little or no 

 mutation occurred in the beef infusion up to 200 hours at 37 0 C. 

 In 0.5 to 1.0 per cent, concentrations of peptone some D — * G 

 change was noted. But when higher concentrations, up to 20 

 per cent., were employed, a very rapid mutation set in, reaching 

 90 per cent, of the total organisms in 96 hours. This was true 

 even when the peptone solutions were made up to volume with 

 beef infusion. Control tubes of undiluted rabbit serum and of 

 beef infusion showed one or two G colonies at 120 hours, but none 

 after 144 hours or after 8 days. This experiment indicates that 

 peptone in suitable concentrations accelerates the D — * G process. 



The G colonies arising in these experiments, and sub-cultured 

 to undiluted rabbit serum, were frequently tested for their dis- 

 tinguishing characters, i.e., low virulence and granular growth in 



