12 BACTERIOPHAGES 



. . . T7, for instance, were collected by Demerec and Fano (1945) 

 and have in common only the ability to infect a strain of Escheri- 

 chia coli known as B. In this instance, but in relatively few 

 others, the phages have been classified by other means. They 

 fall into four groups of "related" phages: Tl ; T2, T4, T6; 

 T5; T3, T7. In this instance the phages within a single group 

 are morphologically identical, and serologically related but not 

 identical. In the following pages we shall frequently speak of re- 

 lated phages, meaning two or more phages having a common 

 host, common morphology, and usually also some common anti- 

 gens. A given "wild-type" phage and its mutants are always 

 related in this sense, as far as is known. In much of the earlier 

 work on phages unclassified specimens, often no longer available, 

 were used. These can only be described as "a staphylococcal 

 phage," or "a coli-dysentery phage." When a phage is re- 

 ferred to by a symbol without indication of host specificity, it is 

 likely to be one of the better known coli-dysentery phages. 

 These remarks will serve to indicate the meaning, or lack of it, of 

 names of phages referred to in this book. General problems of 

 taxonomy are discussed in the final chapter. 



