254 



W. KUNICKI-GOLDFINGER 



in the techniques used and in the bacteria tested. Neverthe- 

 less, some increase was shown in the resistance of bacteria 

 after their exposure to streptomycin in conditions excluding 

 growth. 



In further experiments it was ascertained that the concen- 

 tration of streptomycin in the buffer had no effect on the 

 resulting increase in drug resistance. Furthermore, quite 

 similar results could be obtained when bacteria were suspended 

 in the buffer alone and cooled at 4° C for an appropriate time. 

 The effect of the buffer alone on the increase in resistance is 

 shown in Table III. 



Table III 



Effect of cooling on drug resistance of Esch. coli population (number 



of viable units giving visible colonies on agar-medium containing various 



concentrations of the antibiotic). 



It is thus conclusively shown that for the induction of 

 streptomycin resistance the presence of the drug is not indis- 

 pensable. This fact seems contradictory to Szybalski's hypo- 

 thesis of streptomycin-induced mutation of a total population. 



The results of present research suggest that induction of 

 mutation by streptomycin is not operable in this case. Never- 

 theless the induction of mass-mutation in all cells by other 

 factors, even if improbable, had not yet been excluded. 



In order to test this hypothesis some preliminary experi- 

 ments were made on the stability of resistance. Bacteria 

 incubated in buffer at 4° C in the absence of antibiotics were 

 transferred to beef-heart broth and incubated for various 



