598 EDGAR L. GASTEIGER AND BERRY CAMPBELL 



nerve to a lucite recording chamber, extraneous connective tissue was re- 

 moved, and the nerve ending was crushed to provide an electrical, inactive 

 point for the distal recording electrode. 



Across the recording chamber, 11 silver wires of 20 mils diameter were 

 fixed to support the nerve and sei-ve as stimulating and recording electrodes. 

 By means of a switching system, the stimulus, a thyratron-controlled con- 

 denser discharge, could be applied to the nerve at positions of choice. All 

 stimuli were supramaximal. Throughout the experiment, the point of stimu- 

 lation was alternated from between the sites of irradiation and recording to 

 a point on the opposite side of the irradiation site. In this way, both experi- 

 mental and control recordings could be obtained from the same nerves. In 

 nerves not long enough for recording such "running" controls, a test of the 

 nerve viability could frequently be made after irradiation block by moving 

 the nerve sufficiently to stimulate it just beyond the block or by turning the 

 nerve end-for-end on the electrodes to stimulate an unirradiated portion of 

 the nerve. A third type of control consisted of placing a nerve in the cham- 

 ber without a radiation source and observing the stability of the action 

 potentials over several hours. 



The monophasic action potentials were amplified by an AC differential 

 amplifier with flat frequency response between 10 and 2,000 cycles. They 

 were then photographed from a sweep synchronized oscilloscope. Usually an 

 electrode between stimulating and recording sites was grounded to reduce 

 electrical artifacts. 



Drying of preparations was prevented by flooding the floor of the chamber 

 with Simms solution and by keeping the chamber covered after carefully 

 wetting the nerve on the electrodes. When experiments were performed at 

 higher temperatures (31-38°C) as contrasted to room temperatures (24- 

 29°C), the chamber was placed in an incubator and allowed to equilibrate 

 before beginning irradiation. 



The beta source used in these experiments consisted of small glass bulbs 

 of radon gas, 3 to 4 mm in diameter, with walls thick enough to absorb all 

 alpha particles emitted by the radon decay products. Such bulbs have been 

 commonly used as beta sources for the treatment of eye disease. Their in- 

 tensity was measured in terms of their gamma emission, which has a maxi- 

 mum value of 9% of the total ionization — a negligible amount in these 

 experiments, since the biologic effectiveness of the gammas is relatively 

 very low when contrasted to the betas. The intensity of the beta ionization 

 from these radon sources was compared with that of a strontium standard 

 by means of a scintillation counter, and an average value of 10,000 ± 2,000 

 rep per 100 mc-min was determined.^ In practice both radon-filled bulbs 



' This calibration was made by Mr. J. C. Carlson of the University of Minnesota 

 Hospitals. 



