NATURE OF VIRUSES 13 



fore, claim that viruses probably represent, in a distorted way, 

 the operation of certain cell components. This makes the study 

 of viruses of interest because it may be attacking, in simple 

 form, the problem of single-cell constituents. 



Physics and the Study of Viruses 



The kind of physical methods which may pay off in virus 

 studies are hardly likely to be those of classical physics, involving 

 electrical properties, stress, strain, specific heat, and so on. 

 Rather, the methods of modern physics need to be used. A 

 moment's thought shows that modern physics has progressed by 

 three broad techniques — bombardment, and observation of the 

 consequences, as used in nuclear physics and in atomic-energy- 

 state work; absorption and emission of radiation, as in spectro- 

 scopy of all wavelengths; and scattering of radiation, either as 

 scattering or as diffraction. It is worth a moment to see how 

 these broad techniques can be applied to virus study. 



The methods of nuclear physics — bombardment, and observa- 

 tion of changes — are clearly applicable. Indeed the very same 

 particles — protons, deuterons, alpha particles, and electrons — 

 prove to be highly suitable. The changes produced are not 

 transmutations, but are loss of infectivity, of serological affinity, 

 of absorptive ability, killing power, and interfering power. To 

 each of these a measured cross sectioyi can be assigned, and, as in 

 nuclear physics, the cross section must then be interpreted 

 theoretically. This kind of work is just beginning. 



The second technique — al)sorption and emission of radiation — 

 is obviously confined to absorption. This requires pure virus, 

 and, as it has become available, valuable information regarding 

 ultraviolet absor})tion has been obtained. In some cases this can 

 be combined with polarization studies. The refinement of absorp- 

 tion work includes low-temperature absorption, and very 

 interesting results can be ol)tained in this way. The great sensi- 

 tivity of virus assay enables a second feature of absorption of 

 radiation — loss or change in function — to be measured. This 

 type of study — called the plotting of an action spectrum — is 

 also only in its infancy. 



The third technique — scattering and diffraction — again needs 



