600 



EDGAR L. GASTEIGER AND BERRY CAMPBELL 



100 



CONT 



2000 MC MIN 



4000 



CAT 545 R SURAL 

 222 MC FILTERED 

 T 36* C 



MIN 

 0- 



12- 



18- 



MSEC 



I I I 



Fig. 1. The potentials to the right ilhistrate control and experimental responses 

 from the sural nerve during irradiation with a 222 mc Rn source filtered with a 

 0.1 mm brass foil. Vertical spacing of potentials is proportional to the irradiation 

 time. Decreasing conduction time as irradiation progresses is emphasized by the 

 curving of the lines which connect the potential peaks. To the left, per cent change 

 in activity as measured from amplitude or area of the potentials (see text) is plotted 

 as a function of irradiation time in minutes and dose in millicurie-minutes. In 

 general, these curves tend to be sigmoid, and the smaller fibers of the sural and 

 saphenous nerves were blocked first. 



Illustrations of changes in control and experimental action potentials of 

 the sural and vagal nerves are seen in Figs. 1 and 2, respectively. The poten- 

 tials have been traced one below the other on a time scale which is pro- 

 portional to the period of irradiation. By connecting their peaks, one obtains 

 a picture of the change in conduction velocity as a fimction of irradiation 

 time and fiber type. The slower A fibers show a greater sensitivity to the 

 radiations since their conduction velocities are more markedly reduced. 

 Exploration of irradiated nerves revealed that slowing of conduction oc- 

 curred in less than 1 cm of the nerve, due to the attenuation of beta ray 

 intensity according to the inverse square law. 



To appreciate the change in nerve activity as an experiment progressed, 

 the potential components were plotted as a function of irradiation time in 

 minutes and of dose in millicurie-minutes. The plots in Figs. 1 and 2 

 graphically illustrate changes of the corresponding potentials. An illustration 

 of a similar response of the sural nerve at 27°C is found in Gasteiger's 1959 



