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Structure of Viruses / 1 4 : 2 



many years. Present knowledge indicates that they may be atypical 

 viruses (and, hence, poor standards). Nonetheless, they have been 

 studied so widely that most of the material in this chapter is based on 

 experiments with T phages of E. coli. Figure 1 shows a T phage attached 

 to a bacterial surface. 



Figure I. Electron micrograph of T2 phage particles attached 

 to ghosts of E. coli B. Note that many of the phage particles are 

 attached to the bacterial ghosts by their tails. After T. F. 

 Anderson, American Naturalist 86: 91 (1952). 



2. Phage Studies Using Bacteriological Methods 



The routine method for analyzing bacteriophages involves bacterial 

 plating techniques. To aid in understanding these techniques, the 

 standard assay for determining bacterial concentration is first described. 

 In this method, a large number of Petri dishes are made up with a 

 sterile gelatinous medium on which the bacteria can grow. Each dish 

 is carefully sterilized. One ml of the suspension of bacteria is poured 



