570 MAKOTO SATO, GEORGE AUSTIN, AND WALTER STAHL 



Extracellular response from the afferent fibers showed a gradual decrease 

 in amplitude immediately after an initial dose of 1,270 r. 



Intracellular response from afferent fibers did not show a significant 

 change in amplitude even after irradiation with 10 kr. 



Intracellular response from interneurons did not seem to be affected even 

 by irradiation with 10 kr. 



Extracellular response from motor neurons did not show a significant 

 change in amplitude or in time course for either orthodromic or antidromic 

 stimulations, at least within the first 2 hours after the irradiation at 3,850 r. 

 Thereafter, however, it showed a remarkable increase in amplitude and 

 stayed almost constant more than 1 hour. 



Intracellular responses from motor neurons evoked by orthodromic and 

 antidromic stimulations were not affected significantly, even by irradiation 

 of up to 12 kr, except for a few cases which showed a slight increase in 

 amplitude. 



From these residts, it is inferred that myelinated nerve fibers and cell so- 

 mata in the mammal have a considerable safety factor for the acute effect of 

 irradiation up to 14 kr. 



It is inferred that the sensory nerve is more sensitive to irradiation than 

 the motor nerve, and it is suggested that interneuronal inhibitory passway 

 might also be relatively sensitive to irradiation. 



Acknowledgments 



The authors wish to acknowledge the excellent technical assistance of Mr. 

 Thomas Underwood and Mrs. Evelyn Burkhart in the course of these 

 experiments. 



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