670 



WILLIAM J. ARNOLD 



the head irradiated animals. In one experiment^ all 20 irradiated animals 

 developed tooth overgrowth, supernumerary lower teeth, abnormal breaking 

 off of teeth, and growth of new ones. None of the control animals had tooth 

 defects. The teeth of one of the head-irradiated animals are shown in Fig. 1, 

 photographed approximately 10 months after a dose of 2,500 r. The upper 

 left tooth has grown spirally through more than 360 degrees, penetrating the 

 roof of the mouth and emerging at the side of the nose. The lower right 

 tooth penetrates the roof of the mouth. Later work, in which control animals 

 were starved to match the weight loss of irradiated rats, indicates that these 

 deformities were a primary result of irradiation rather than a secondary 

 effect of not eating. 



Emotional Behavior 



In one experiment, 40 pied rats were divided into split-litter control and 

 experimental groups of 20 each with 10 males and 10 females in each group. 

 In the second experiment, 16 Sprague-Dawley male rats were randomly 

 assigned to experimental and control groups of 8 each. The apparatus con- 

 sisted of an "open field" constructed by surrounding a circular area 10 ft. 

 in diameter with a sheet metal barrier 24 in. high. This area was brightly 

 illuminated by a light suspended above its center. 



Test trials were given 5 days prior to irradiation and at 5 day intervals 

 after irradiation for 30 days. In the first experiment, a final test trial was 



Fig. 1. Tooth deformities developed during 10 months after 2,500 r head ir- 

 radiation. 



