ANDRE LWOFF AND ANTOINETTE GUT MANN 



that the inducing factor intervenes in the course of the development of the 

 mother culture. The drop technique, in spite of long and laborious experiments, 

 did not bring the solution to this problem, which was then taken up with ordinary- 

 cultures. Since that time, experiments (A. Lwoff, L. Siminovitch, and N. 

 Kjeldgaard) have shown that it is possible to achieve conditions which induce the 

 lysis of 20 to 30% of a bacterial culture and that this lysis is accompanied by the 

 liberation of bacteriophages. These experiments shall be described in a separate 

 communication. We shall content ourselves here with a discussion of the 

 conclusions to which these experiments led, that is to say, that the production of 

 bacteriophages is induced by external factors. 



The Hypothesis of Burnet and McKie. F. Burnet and M. McKie (1929b) 

 realized that all bacteria of the lysogenic strain contain in their hereditary 

 constitution a unit which is potentially capable of liberating bacteriophages; 

 that these bacteriophages can be liberated during the process of normal growth; 

 that activation of the hereditary structure must take place spontaneously for 

 there to be any liberation of bacteriophages; that the data do not allow one to 

 infer whether or not there is an intracellular activation; that the conditions are 

 probably analogous to those which intervene in monomolecular reactions or in 

 radioactive disintegrations. Undoubtedly, some of these concepts did not stand 

 up to the test of time. But the problem was remarkably well stated. And the 

 hypothesis of "activation" should have merited better than a complete indif- 

 ference. 



Everything seems to indicate that the bacteriophage possesses a remarkable 

 attractive power. It inhibits, in effect, bacterial growth, detours to its own end 

 the metabolites necessary for enzymatic adaptation (J. Monod and E. Woll- 

 man, 1947) and growth of a different bacteriophage (M. Delbriick and 

 S. E. Luria, 1942; A. D. Hershey and R. Rotman, 1948). H. J. MuUer (1947), 

 while discussing the problem of the reproduction of the gene, concluded that only 

 the phenomena of long range forces could account for the duplication. Perhaps 

 the attractive power of bacteriophages is of this same type. 



Let us suppose that in a lysogenic bacterium the probacteriophage, under 

 whatever form it might exist, is in competition with a certain number of other 

 particles. In potentially lysogenic bacteria that equilibrium is stable. But if, 

 for one reason or another, the equilibrium is perturbed possibly because the 

 attractive power of the bacterial particles is diminished or because the attractive 

 power of the probacteriophage is increased, the latter will develop and give rise 

 to bacterial virus particles. More concretely and simply, one might envisage 

 that the "key enzyme" necessary for bacteriophage synthesis, which M. Delbriick 

 and S. E. Luria (1942) have postulated in order to explain the phenomenon of 

 interference, becomes available; perhaps, because the normal substrate of this 

 enzyme ceases to be synthesized. Let us note in passing that this defect of sub- 

 strate synthesis could as well be the consequence of a mutation as a change of 

 the conditions of the medium. In any case, the association or combination of this 

 key enzyme with the probacteriophage would then set off the process of mul- 

 tiplication. 



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