IX. METABOLISM 293 



some conditions which might act as a stimulus to activate the proto- 

 plasm to accumulate or synthesize nucleic acid, and under which the 

 vigorous multiplication was desirable for the organism. Therefore, the 

 organisms which could accumulate RNA under such conditions might 

 become fitter and left as such. 



As is well known, the nucleic acid which will accumulate in 

 bacterial cell after the infection with phage is DNA; the RNA content 

 of the host remaining constant. This may result in the relatively 

 long persistence of the unbalance of the ratio, and at the same time 

 this should be favourable for the liberated protoplasm particles to act 

 as the virus, if not for the bacteria themselves to act as living or- 

 ganisms. This property of bacteria to accumulate DNA on the virus 

 infection might contribute not only to the virus multiplication but 

 also to the evolution of the bacteria themselves, because the property 

 to make the virus pattern rigid is to make the superior pattern of 

 others spread easily. 



3. Dimensions of the Mass of Assimilase with Special 

 Reference to Protein Synthesis 



The chemical analysis of the cytoplasmic particles, such as micro- 

 somes and mitochondria, shows that they contain ribonucleic acid in 

 rich amount, and it is evident that these particles account for a very 

 large proportion of cytoplasmic ribonucleic acid. It has been suggested 

 that protein synthesis is mainly connected with such particles, which 

 are therefore recognized as the fundamental units of living organisms 

 having the power of self duplication (8) (26). 



It is evident, however, that each separate particle has no faculty 

 of synthesizing protein and accordingly not selfduplicating, because 

 as is generally accepted viruses cannot multiply outside the living 

 cells. Nor any one has succeeded in making the cytoplasmic particles 

 isolated from the cell multiply in vitro. Even the ability for incor- 

 poration of protein molecules is lacking in viruses, an ability which 

 is not attained until they reach the stage of Rickettsiae. As already 

 mentioned, a certain type of Rickettsiae can multiply outside the host 

 if blood plasm is added to the media. 



This ability seems intimately related to the dimension of the 

 mass of assimilase or of the microorganisms, for as discussed in Part 

 I assimilase action is, to some extent, a function of the size of the 

 assimilase or the degree of polymerization of proteins. For the func- 

 tion of synthesizing the protein from amino acids may be needed still 

 greater dimensions. Rickettsiae, pleuropneumonia-organisms, and re- 



