246 BIOLOGICAL EFFECTS OF IONIZING RADIATIONS 



subject, one can only say that the possibilities exist, and should be remem- 

 bered during discussions of the physiological effects, which are currently 

 receiving more attention. 



Fluidity (Inverse of Viscosity). Most of the useful information on the ef- 

 fects of ionized radiations on fluidity (ease of flow in response to a physical 

 force) has been done either on plastics or on aqueous solutions of big 

 molecules. 



From the former it has been learned that cross-linking of polythene by ir- 

 radiation increases markedly its melting point and increases its elasticity. 

 By contrast, irradiation of teflon (a fluorinated and inert organic) leads to 

 hardening and embrittlement, and loss of elasticity. This might lead one to 

 anticipate similar effects in elastomeric tissue in the walls of blood vessels, 

 were it not for the fact that the effects are exhibited only after the absorption 

 of a few million rads! 



On the other hand, the fluidity of aqueous solutions of biologically active 

 molecules has been intensively studied, especially as a technique of measur- 

 ing the change in molecular weight effected by radiations. Like diffusion, 

 many examples are known in which cross-polymerization is important, and 

 many in which molecular rupture is to be inferred. 



Electrical Conductivity. In body fluids the conductivity is high. Irradiation 

 makes no detectable change. 



It is in the inner, fatty-acid or lipid part of the living membrane (Figure 

 6-7) that we expect a change in conductivity. The lipid, an oil, has very low 

 conductivity. Analogy with polythene or lucite may be useful as a guide. 

 These materials break down internally under irradiation, such that electrons 

 are knocked off one part of the molecule and caught or trapped elsewhere, 

 leaving a positive site behind. The conductivity increases, because the 

 charges are somewhat mobile, and a steady-state concentration, higher the 

 higher the dose rate, is set up and maintained. Upon cessation of the radia- 

 tion, the charges recombine slowly, and the conductivity drops to its original 

 value. Although the k for these substances is very, very small (~10~ 21 

 ohm -1 cm '), it is raised as much as fifty thousand times by an X-ray dose 

 of only 8 roentgens (r) per min. By comparison, the conductivity of a resting 

 nerve membrane is of the order of 10~ 12 ohm "' cm ', due almost entirely 

 to the lipid inner layer. 



The "activation" of nerves by radiations, and some effects on the central 

 nervous system, to be discussed in the next section, indicate that enhanced 

 electrical conductivity may be one of the most important biophysical effects 

 of ionizing radiations. 



Chemical Reactivity 



The effects of ionizing radiations on the rate of chemical reactions could 

 be inferred from knowledge of the factors upon which rate depends. In gen- 



