248 IV. THE PRINCIPLES OF LIFE PHENOMENA 



infected with phage undergo lysis with the liberation of phage-like 

 particles which have no phage activity. The ultraviolet absorption 

 Coefficient of these particles revealed that their nucleic acid content, 

 if any, is much lower than that of usual phage particles (35). 



Bacterial strains having acquired increased resistance to the lethal 

 effects of X-rays or ultraviolet rays have been found to synthesize 

 several times as much DNA as do the sensitive strains (36). Such 

 bacterial sfrains might have increased the resistance, because they 

 have undergone a structural change to cause the increase in DNA. 



In the presence of cobalt ions the growth of some bacteria is 

 prevented but RNA content may be raised (37), and certain other 

 bacteria, when grown under unfavourable conditions, may accumulate 

 large amount of RNA (38). It is considered that also in these cases 

 there might occur structural changes which caused the alteration in 

 the mixed proportion. 



2. Plasmagenes 



A number of workers claim that the characters of organisms are 

 determined not only by genes but also by cytoplasmic particles 

 designated as plasmagenes. In the theory of the writer, it may be 

 said that protoplasm is composed of a sort of genes, since all the 

 elementary bodies of protoplasm are assimilases capable of exhi- 

 biting a function like a gene. However, as the bodies present in the 

 nucleus possess the strongest assimilase action in the cell, the pattern 

 of the whole protoplasm is usually directed by such bodies, which are 

 accordingly called genes. It may be possible, therefore, that some 

 cytoplasmic particles attain to the supremacy if the genes proper ex- 

 hibit only a weak effect. 



A factor called kappa found by Sonneborn (39) in Paramecium 

 was regarded as a kind of plasmagenes. This factor can exhibit a 

 strong influence on protoplasm structure of this protozoan and provides 

 the protozoan with the faculty to produce a substance named paramecin. 

 As this substance can kill a sensitive strain of the protozoan, the indi- 

 viduals producing paramecin are named killer. In short, kappa seems 

 to be able to overcome the genes proper to direct the structure of the 

 protoplasm. As a result the property to produce paramecin arises, but 

 in the presence of some strong genes kappa fails to exhibit its influ- 

 ence and is perished. 



This factor, however, now appears to possess many characteristics 

 of microorganisms such as a Rickettsia (40). The size of the factor is 

 similar to that of Rickettsiae, being 0.2 to 0.8 ix. In addition, it should 



