OTHER CHARACTERS OF THE PHAGES 



331 



Fig. 50. — Electron micrographs of a Bad coli. phage. ( X 53,000). 

 (From a photograph kindly supplied by Dr. S. E. Luria) 



protein into an aggregate that in concentrated solutions behaves in lysis, in the 

 photographic field, in the ultracentrifuge and in the ultrafilter as a unit particle. 

 The titration of lytic activity by the plaque method thus reveals only one in thirty 

 of the sub-units. The lytic unit readily dissociates into diffusing particles, also 

 containing carrier protein, which in turn are made up of ultimate particles having 

 a particle weight of 50,000. If these facts are confirmed, then the chemical descrip- 

 tions of phage as a nucleo-protein (see Schlesinger 1934, Northrop 1938) may 

 prove to be descriptions of carrier protein only. The identity of the protein 

 isolated from phage preparations with phage itself has already been questioned 

 on technical grounds (see Moriyama and Ohashi 1937, Flu 19386). 



The justifiable inferences from all these observations take us far beyond the 

 conclusion that the phage is particulate. They accord well with the view that 

 phages are filtrable viruses. They accord badly with any other hypothesis that 

 has yet been propounded. A particulate lytic agent might conceivably consist of 

 particles of bacterial protoplasm on to which some active principle had been 

 adsorbed. If so, the adsorbing material, and the nature of the complex formed, 

 must be specific for each phage in a high degree, or the particles resulting from 

 disruption of a bacterium by one type of phage would be of varying sizes, and 

 would be unlikely to differ consistently in size from those produced by the action 

 of another phage. 

 Other Characters of the Phages. 



Most phages, within the pH range over which they remain active, appear to 

 carry a negative electric charge, in this way resembling bacteria and filtrable viruses 

 (Todd 1927, Krueger et al. 1929, Burnet and McKie 1930a, Natarajan and Hyde 

 1930). 



