VII. THE MODE OF VIRUS MULTIPLICATION 93 



2. The Difference in Nucleic Acid Content between Virus 

 and Host Cell Protoplasm 



There should be, and actually is, an intimate relation between 

 virus and its host cell protoplasm in chemical compositions, but, on 

 the other hand, there are claims that considerable differences are 

 present between them. The differences are believed to be found in the 

 main in both the kind and content of nucleic acids. 



According to the chemical analysis of a strain of phage of E. coli 

 by Csaky et al. (113) the virus consists of nucleic acids about 40 per 

 cent, while the host bacteria only about 5 per cent. Such a striking 

 difference may be mainly attributed to the isolation of peculiar parti- 

 cles wdth high nucleic acid content which are regarded as sole phage 

 particles, because the particles with high nucleic acid content appear 

 to sediment more rapidly than those containing a little or no nucleic 

 acids. According to Markham and Smith (50) the purified preparation 

 of turnip-yellow mosaic virus protein separates into two parts on the 

 application of ultracentrifugation ; the bottom component contains 

 nucleic acid, while the top is nucleic acid free, although these two 

 components have the same electrophoretic mobility and isoelectric 

 point, and both crystallizing in the same crystalline forms. 



Phosphorus content in a phage preparation isolated by our method 

 was found to be 1.28 per cent, so that nucleic acid content in this 

 preparation at most could not be greater than 13 per cent. This value 

 is much lower as compared with that of phage particles isolated by 

 means of ultracentrifuge by a number of w^orkers. It must be borne in 

 mind that all the particles present in the culture filtrate are to be iso- 

 lated by our method, while this is not the case with the isolation by 

 the ultracentrifugation. Again, the protoplasm, in general, contains a 

 considerable amount of lipids, about one third of it being lipids. The 

 phage particles obtained by our method likewise show a high content 

 of lipids and also its one third was proved to be lipids, whereas 

 lipid content of phage obtained by means of ultracentrifugation has 

 been reported to be very low ; according to Csaky et al. it was only 

 about 1 per cent. The lower is the lipid content, the sedimentation 

 rate may be the greater, and the reverse may hold true for nucleic 

 acids. 



Extremely small yields of virus particles by means of ultracentri- 

 fugation are also indicating that the particles isolated by this method 

 are only a portion of the particles produced by the decomposition of 

 the protoplasm on the infection. 



