192 A. LWOFF 



apparatus. Tliis means that Escherichia coli, for example, and the hypotlie- 

 tical parasitic bacterium which is supposed to have degenerated into a 

 prophage have a common ancestor. In other terms, the genetic material of 

 E. coli and the genetic material of the prophage have originated from the 

 very same genetic material. And the common structure, which has been 

 preserved in the bacterial chromosome as a receptor, and in the genetic 

 material of the temperate phage where it accounts for lysogenization, is 

 the signature of the common origin. 



If one admits that the genetic material of the prophage had its origin in 

 the genetic material of a given bacterium, it could as weU have originated in 

 another one and especially, as pointed out by S. E. Luria, in an ancestor of 

 the very bacterium which is now lysogenic. The phase at which evolution has 

 taken place is not as important as the existence of a common origin. The 

 endogenous and exogenous theories can be reconciled in the following 

 formula: the genetic material of the bacteriophage and the genetic material 

 of the bacterium have evolved from a common structure, the genetic material 

 of a primitive bacterium. 



Whatever the unknown ways might have been by which a bacteriophage 

 has evolved from something which was not the present-time bacteriophage, 

 it has now reached a certain state; it now exhibits certain features which 

 have to be considered independently of their possible origin. 



IV. Is Bacteriophage an Organism? 



Organisms might be visualized as independent units of iategrated struc- 

 tures and functions. Is bacteriophage an organism? 



Let us examine and compare the bacteriophage on the one hand, and, on 

 the other hand, a typical microorganism, such as protozoon, a yeast, or a 

 bacterium. 



1. AU typical microorganisms contain both types of nucleic acids, DNA and 

 ENA. Bacteriophage contains only one type.^ 



2. All typical microorganisms are reproduced from the integrated sum of 

 their constitutive parts — nucleus, cytoplasm, cytoplasmic organelles, and 

 cortex. Bacteriophage is produced or reproduced from its genetic material. 



3. The essence of the multiplication of any cell or microorganism is the 

 replication of the genetic material, but multij)lication is not separable from 

 growth, which is the result of the synthesis of ceU material. During the 

 growth of a microorganism, the individuality of the whole is maintained. 

 Growth culminates in binary fission. An individual molecule cannot undergo 

 fission. The replication of nucleic acid by the template mechanism is not a 



^ This might be true only for the proviral and the! nfective phase, not for the vegeta- 

 tive phase. 



