294 C. T. GAFFEY 



ative steps due to radiation take place rapidly and could be interpreted as a 

 full loss of the membranes' helical molecules capacity to change states, per- 

 haps as a result of a loosening of their structure. This would cause a broad- 

 ening and flattening of the channel size distribution curve, which in essence 

 eliminates selective ion permeability, thus producing a rapid loss of excitability. 

 In conclusion, it can be argued that certain doses of radiation are thresh- 

 old for neural injury as a result of the membrane's macromolecules being 

 irreversibly impaired in their ability to change states. 



Summary 



Isolated sciatic neives from Rana pipiens were exposed to cyclotron ac- 

 celerated beams of 455 Mev deuterons and 910 Mev alpha particles. The 

 degree of electro-physiologic damage was found to depend on the dose of 

 irradiation and the elapsed time from irradiation. 



With massive doses of alpha particle or deuterons (greater than 300 krad) 

 the action potential of the frog's sciatic nerve was promptly suppressed. 



Within the range 30 to 300 krad for alpha particles and 60 to 300 krad for 

 deuterons, the survival time of the action potential was a logarithmic func- 

 tion of the absorbed dose. 



Alpha particles were found to have twice the relative biologic efTectiveness 

 of deuterons in blocking excitation. 



An increase in the refractory period was manifested before conduction 

 velocity reduction, action potential depression, latency period prolongation, 

 and stimulus strength alteration in the high energy irradiated nerve. 



Alpha particle irradiated nerves were shown not to increase in sodium ion 

 permeability for doses less than 150 krad. Between 150-200 krad the rate of 

 Na^^ penetration was slightly increased, while the rate of loss of Na-- from 

 the nerve was decreased. 



Variations in the exposure rate from 0.5 to 8.0 krad per min failed to 

 induce a dose-rate effect for alpha particles. 



The inhibition of neural activity resulting from alpha particle and deu- 

 teron irradiation was not reversible. 



A model for the neural membrane was outlined, and the action of radia- 

 tion was interpreted on the basis of this model. 



References 



Audiat, J. 1932. Action du rayonnement x sur les parametres d'excitabile du nerf. 



Compt. rend. soc. biol. 110, 365-367. 

 Audiat, J., and Piffault, C. 1934. Action des rayons x sur le nerf isole. Compt. rend. 



soc. biol. 116, 1270-1273. 



