A. D. HERSHEY 



MATURATION 

 VEGETATIVE RESTING 



PHAGE PHAGE 



RESTING PHAGE 

 Figure 1. 



RESTING PHAGE 



Extracellular virus is called resting because it is stable and 

 metabolically inert. Purified preparations of T2 consist of 

 uniform tadpole-shaped particles with a polyhedral head meas- 

 uring about 0.1 micron across, and a tail about 0.1 micron long 

 and perhaps one-fourth as broad (2,67). The surfaces of the 

 head and tail contain distinct antigenic proteins (36). One 

 particle contains about 2 X 10~^° 7 of deoxypentose nucleic 

 acid (DNA) (6,28), which can be expelled by osmotic shock 

 leaving a proteinaceous ghost that retains the shape and some 

 of the biological properties of the intact particle (1,21). The 

 ratio of protein to DNA in the whole particle is about one to one. 

 The DNA is variously reported to be released in the free state 

 (23), or combined with protein (62). 



The proteins of T2 differ antigenically from the proteins of 

 the host. The DNA of T2 contains 5-hydroxymethyl cytosine 

 but no cytosine (69), in which respects it differs from all known 

 examples of DNA from other organisms. Both facts suggest 

 that virus and bacterium have pursued separate, though not 

 independent, evolutionary paths for a long time. Otherwise 

 these facts can be regarded as analytical aids pure and simple. 



INJECTION 



When a particle of T2 makes its specific, irreversible at- 

 tachment to a bacterium (living or dead), the viral DNA passes 

 into the cell, leaving the empty protein shell outside (27). This 

 husk may now be seen adhering to the cell by the end of its tail 



