GENERAL DISCUSSION 155 



death than rats. Our rats did well with 5,000 r cumulative total head exposure at 

 the end of 228 days, provided they were not stressed as they were when they were 

 placed in the Skinner box and tested for positive food reward. To reply to Dr. 

 Peacock's question: to our way of thinking this change in the animal's behavior 

 as related to its performance in the Skinner box was one that seemed to be motiva- 

 tion. We tested our animals between and after each dosage and following the end 

 of the first 5 weeks on food intake. The food intake of the x-irradiated animals 

 versus the controls was not so different as to make us think that this was the whole 

 picture. The controls when placed on a deprivation diet maintained their normal 

 weight, which tended to climb slowly. We believe there is a definite food problem 

 involved, but there may have been one of motivation also. We are now utilizing 

 shock avoidance and positive food reward together in anticipation that this will 

 help clarify the matter. 



John L. Falk (Harvard School of Public Health, Boston, Massachusetts): 

 I was happy to see that Dr. Brownson was using long-term testing. Short-term tests 

 involving food intake or various food-motivated performances might cause radia- 

 tion sickness. Did Dr. Brownson use a variable interval schedule? We have been 

 making readings in medial nuclei of the hypothalamus and getting increases in 

 bar-pressing rates on variable interval schedules. Since there did seem to be some 

 hypothalamic involvement in Dr. Brownson 's animals, I wonder if perhaps there 

 was more involvement in the lateral nuclei, possibly indicating classical aphagia? 



Robert H. Brownson : I think the only answer we will have to this question 

 is dependent on the results obtained with shock avoidance. We anticipate improved 

 testing methods in our future plans. The schedule was aperiodic, and the tapes 

 were run for 45-minute intervals. The periods ran 4-224 seconds apart with an 

 average of 62 seconds between reinforcements. 



Cornelius A. Tobias (University of California, Berkeley, California): I had the 

 pleasure of discussing with Dr. Barlow his interesting statistical findings and trying 

 to encourage him and other people who are taking a similar approach to the 

 explanation of some diseases similar to this as to etiology. However, there are 

 several aspects that need further study and improvement. It seems to me that if 

 multiple sclerosis is due to radiation, it is most likely that it should be due to early 

 effects in the embryologic or even germ cell stage. It appears that neither the 

 studies by Dr. Hicks nor Dr. Rugh show that multiple sclerosis is a frequent 

 occurrence in animals developing from irradiated embryos or germ cells. Secondly, 

 findings such as these should be correlated with other findings which were also 

 discussed in Dr. Rugh's paper. For example, those by Gentry, who finds that in 

 certain areas of the United States with high natural radioactivity background 

 congenital malformations occur more frequently than elsewhere. If the Barlow 

 and Gentry studies do not correlate, then it would seem that it is not the low 

 ionizing component of cosmic rays that would cause the effect in multiple sclerosis, 

 but some other component of cosmic radiation that occurs perhaps only rarely. 

 There are some cosmic ray phenomena for which further work may be needed 

 before correlations can be established. For example, the so-called Auger showers 

 which are energetic showers arrive at ground level from primary cosmic rays which 

 can give well measurable doses to a single individual. On the average one such 



