A. H. DOERMANN 653 



(Fig. 3). The increase of infective centers in comparable cultures (Fig. 2) at 

 these later stages is probably brought about by liberation of phage particles 

 concurrent with this lysis. 



Experiments Using 5-Methyltryptophan as the Metabolic Inhibitor. — In trying 

 to find a suitable metabolic inhibitor for instantaneously stopping phage 

 growth, a large number of experiments was done using the antimetabolite 

 5-methyltryptophan (5MT)- whose bacteriostatic action is blocked by trypto- 

 phan (9). The technique used was similar to the cyanide lysis procedure except 

 that tryptophan was omitted from the lysing medium and 5MT was used in 

 place of cyanide. The results (?'ig. 4) are quite similar to the cyanide results in 

 all respects except one. They are similar in failure to recover any phage particles 

 during the early stages of the latent period, in the difiference between single and 

 multiple infection, and in the shapes of the curves. They are different, however, 

 in that both the single and the multiple infection curves are moved to the left 

 along the time scale by 3 to 4 minutes. This indicates that more phage is liber- 

 ated per cell if lysis is induced in the presence of 5MT than if it is brought about 

 in the presence of CN~. This difference may be interpreted on the basis of two 

 alternative hypotheses. 



First, it might be suspected that CN~ penetrates the cell and reaches its site 

 of inhibition more quickly than 5MT. This would allow more phage repro- 

 duction to go on between the time of exposure to the 5MT and the time at 

 which the cell breaks open. In this event, a higher concentration of 5MT would 

 enable penetration of an inhibitory amount in a shorter period of time, thus 

 reducing the amount of phage found. To test this, the concentration of 5MT in 

 the lysing medium was increased fivefold. No difference in the amount of phage 

 liberated was found, suggesting that the rate of penetration of the poison is not 

 limiting its effectiveness. 



A second hypothesis is that the reaction blocked by 5MT may be one of the 

 earlier ones involved in the synthesis of phage constituents. At the time of 

 addition of 5MT many individual phages may already have acquired these 

 constituents and thus be able to go on to maturity before lysis disperses the 

 enzyme equipment of the infected cell. Cyanide, on the other hand, may block 

 one of the terminal reactions in phage production, with the result that at a 

 given time fewer individuals will have passed this reaction than will have passed 

 the 5MT-inhibitable step. Consequently, fewer particles will be liberated when 

 using cyanide than when 5MT is used. 



DISCUSSION 



Earlier experiments (2) and tests made of the lysing efficiency of the T6 

 stocks used here indicate that rapid lysis occurs when T6 stocks are added in 



^ Obtained through the courtesy of Dr. M. L. Tainter, Sterling-VVinthrop Research 

 Institute, Rensselaer, New York. 



83 



