268 IV. THE PRINCIPLES OF LIFE PHENOMENA 



but at the same time it may equally be possible to regard them as 

 spores or primitive gametes, and so the combination may be said to 

 be a primitive form of the sexual conjugation. 



However, since in such a conjugation the weaker individual is 

 completely defeated, the stronger one will be unable to adopt any 

 specific character of the former, although it can anyhow accomplish 

 rejuvenation through the contact with different structure. If a part 

 of the structure of the weaker individual was intermixed with that 

 of the stronger by this conjugation, an individual having a new 

 character would be produced, with a much contribution to the advance- 

 ment of the evolution. 



This state of affairs would possibly result when protein structures 

 of nucleic acid-rich particles of primeval organisms were differentiated 

 to some extent. With certain bacteria the presence of such a differ- 

 entiated structure is actually confirmed. As was already described, 

 if two different viruses, A and B, affect simultaneously a strain of 

 bacteria, sometimes a new virus is produced which has peculiarities 

 of both A and B. Instead of two kinds of viruses, two types of 

 bacteria yield the same result ; the conjugation of two strains of 

 bacteria occasionally produces a new strain of bacteria which' have 

 the characteristics of both strains. 



Thus Lederberg and Tatum (77) (78) have actually demonstrated 

 such a sexual reproduction of bacteria. They have made use of 

 biochemical mutant strain which are unable to synthesize certain 

 essential substances and which consequently can grow only on media 

 to which those substances have been added as nutrients. For example, 

 one strain used was unable to synthesize biotin and methionine, ano- 

 ther prolin and threonine. When two such double mutants are grown 

 in mixtures in minimal medium, lacking the nutrients above mention- 

 ed, there appear appreciable numbers of structural recombinations 

 ^which can synthesize all the enumerated substances and consequently 

 survive. Lederberg has also made use of strains which differ in 

 the ability or inability to ferment lactose, and in resistance or suscepti- 

 bility to a specific bacterial viruses. 



In this case also protoplasm particles can substitute the bacterial 

 cells as has been demonstrated by Hayes (79) who has found that 

 sexual conjugation of bacteria can be achieved by a virus-like agent. 

 These particles, therefore, should be regarded as primitive gametes. 

 However, both individuals may be unable to make use of such particles 

 for their sexual reproduction, since the multiplication of the structure 

 fails to be accomplished by the combination of two particles only, and 

 so for the multiplication, one of them should be present in a cell or 

 at least should be present in combining with large amount of 



