14 : 1/ Structure of Viruses 



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electron microscopy, ultracentrifugation, spectrophotometry, and ioniz- 

 ing radiation. Although one can certainly use any of these without a 

 knowledge of physics, it is also true that people with an inclination 

 toward physics tend to feel more comfortable using these study tools. A 

 third reason, albeit less important, is that many phases of virus research 

 have involved mathematical manipulations of the data of a complex 

 nature that appeals to certain physicists. 



The existence of viruses, as well as many of their basic characteristics, 

 however, were discovered by "pure" biologists. After it was established 

 that bacteria and other microorganisms caused human (and animal) 

 diseases, occasional cases were found in which no organisms of a micro- 

 scopically visible size were associated with a disease. Eventually, it was 

 discovered that diseases of this type even killed bacteria. The latter 

 could be studied conveniently by conventional bacteriological tech- 

 niques; the destructive agents were called bacteriophages. 



The size, shape, and weight of viruses remained unknown until the 

 development of modern physical equipment. In Table I are listed some 



TABLE I 



properties of a few viruses and bacteriophages. Those of the so-called 

 "T series," which act on the bacterial species Escherichia coli, are all listed 

 since these have been used in many studies. The T phages have the 

 advantage that work in one laboratory can be compared with that in 

 another; these T phages have been the "standard" for virus research for 



