SIZE AND MORPHOLOGY OF BACTERIOPHAGES 37 



Microscopic measurement of size of virus particles is com- 

 plicated by shrinkage and distortion on drying, increase of size 

 by shadowing with metals, and difficulties in calibration. These 

 difficulties have been minimized in various ways (Anderson, 

 1951 ; Williams, 1953). Some very careful measurements have 

 been published by Williams and Fraser (1953). Estimates of 



Figure 1. Phages of diverse morphology. Left, phage 1'3, unpurified 

 lysate. X 46,000. UnpubHshed. Right, two phages carried by a lysogenic 

 strain of Bacillus cereus (Kellenberger and Kellenberger, 1952). Unpurified 

 lysate, X 40,000. Unpublished. 



particle size of several bacteriophages by electron microscopy 

 and other methods are given in Table II. 



Further information about the structure of several phages has 

 been obtained by degradation of the particles in various ways. 

 Coliphage T2 and its relatives, and the staphylococcal phage K, 

 are subject to osmotic shock (Anderson, 1949; Hotchin, 1954). 

 To observe this, the phages are suspended in concentrated solu- 

 tions of sodium chloride and, a few minutes later, water is 

 dumped in. The phage particles lose their characteristic in- 

 fectivity. Microscopic examination now reveals empty, but 

 more or less intact, phage ghosts. Herriott (1951a) showed that 

 the ghosts, after treatment with deoxyribonuclease, contained 



