The Biochemistry of Lysogeny 39 



aptitude of the organisms was diminished. After prolonged immersion, 

 the inaptitude became more pronounced. 5 



The starvation medium was found to be at pH 5, but the hydrogen- 

 ion concentration could not have contributed to inaptitude for it was 

 found that the pH of cultures in logarithmic growth phase could be 

 lowered to 5 with HC1 and, even though the organisms were kept at 

 that pH for 3 hours, their aptitude was not suppressed. A variety of 

 acidic metabolites which might have accumulated into the starvation 

 medium were tested for their effect on aptitude. Fumaric acid at a 

 concentration of 0.005 M suppressed aptitude, provided the pH was 

 kept at 5. An assay of the starvation medium for fumaric acid by 

 Racker's method indicated the absence of the acid at anywhere near 

 the effective concentration. Nevertheless, the suppression of the apti- 

 tude by fumaric acid was studied in some detail; it did not appear to 

 consist merely of a screening of the irradiation, for it was highly pH 

 dependent and quite specific: the higher homolog, glutaconic acid, was 

 found to be ineffective." Derivatives of fumaric acid which could not 

 dissociate, i.e., the diamide, the diglycyl, and the diglutamyl derivative, 

 were prepared, and it was found that these suppressed aptitude at 

 pH 6.5 as well. Thus the low pH needed for fumaric acid to be effec- 

 tive as a suppressor of aptitude was necessary to repress the ionization 

 of the acid rather than for any effect on the microorganism. It was 

 found that all of the above fumaric acid derivatives are screening- 

 agents against irradiation if the irradiation is passed through them, 

 via a quartz dish, when they are out of contact with the microorganism, 

 but they are particularly potent in contact with the organisms. The 

 phenomenon thus seemed to resolve itself into a curiously effective 

 screening by these compounds (by concentration on the bacterial cell?) 

 — and, since it appeared to be not related to aptitude, work on it was 

 shelved. 



On return to the study of the starvation medium itself, it was found 

 that it absorbed very strongly at 260 m/x. A cursory examination by 

 elution chromatography revealed the presence of a variety of nucleic- 

 acid fragments. The only similar observation we could find in the 

 literature was a brief posthumous note by the late Dr. Marjory 

 Stephenson who found in a study of autolytic ribonuclease in E. coli 

 that acid-soluble phosphorus accumulated in the buffer medium in 

 which the organisms had been suspended. 7 We therefore investigated 

 the phenomenon in some detail to determine whether the excretion of 

 nucleic acid fragments is a concomitant of all types of starvation, 

 whether it is limited only to some bacterial species, or whether it is. 



