CHAPTER XXII 



PHAGE TAXONOMY 



Essential for any serious study involving many different ob- 

 jects is the classification of the objects into well defined categories 

 and the development of a nomenclature to designate these cate- 

 gories. Because it is generally accepted that bacteriophages are 

 to be included among the living organisms it seems that the ulti- 

 mate aim should be to apply to the bacteriophages the Linnean 

 scheme of classification. With this in mind we will inquire 

 briefly into the principles of taxonomy. 



1. Purpose and Principles of Taxonomy 



The purpose of taxonomy is to give an appropriate and gen- 

 erally acceptable name to each distinct variety of organism, and 

 to place these \'arieties in a hierarchy of ever larger groups, to in- 

 dicate their natural relationships to one another. In the original 

 Linnean classification the natural relationships were based on 

 morphological resemblances. With the development of the con- 

 cept of evolution and the sciences of paleontology and genetics, 

 the Linnaean categories acquired a phylogenetic significance so 

 that natural relationships implied a common ancestry, more or 

 less remote in time. 



The basic category of the taxonomist is the species, which may 

 be defined as a group of interbreeding natural populations that 

 is reproductively isolated from other such groups. The inter- 

 breeding test makes the species a readily delimited category in 

 sexually reproducing organisms. The lack of such a test has re- 

 sulted in the taxonomic abominations so prevalent in the field of 

 microbiology. For instance, Bergey's Manual (Breed, Murray, 

 and Hitchens, 1948) lists 150 species in the genus Salmonella. 



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